Your device is still under warranty. Before you do ANYTHING to repair this machine or it's components, internal or external... Call Apple. They will replace anything that is not operating properly that is no fault of yours, but a fault of the equipment.

You're not going to like what I'm about to say..... You have two most likely scenarios here. First, run an AHT. (Boot the device holding the "D" key to get to the menu. Some devices on the borderline need opt + D if holding just "D" doesn't work) If all checks out there... you'll need to wipe and reinstall the OS. It should not take your machine near anything close to 12 hours for an OS install. I just installed a fresh copy of Lion, then Mountain Lion...then Mavericks (before I realized my machine rated for El Capitan)... then El Capitan... on a 2008 15" MBP core duo with 4GB of RAM... and the whole process (because of my goof) took my machine 4 hours. First of all, make sure that all of your hardware you replaces is rated for your machine. i.e. the SDD, make sure that the RAM clock speed is rated for your machine, etc. Given that it took so long...and you're getting incredibly slow response times... I would say that either your RAM or SDD is faulty. Run the AHT. If you get bad results, then you know 100%...

First of all, are you getting any strange tones when it tries to start back up? I know most people would mention this if it did, but you'd be surprised. Those tones are error codes that he machine gives you. Are you getting any strange text across the screen with a strange grey background? (Kernel Panic) My best guess with limited information on any behavior other than freezing and restarting itself is a RAM issue. If the RAM locks up, it could shut itself down (or restart) to prevent any real damage that can occur during a lockup. Try following the steps for a PRAM (NAVRAM) reset. Power down your machine.... and remove all peripherals. - Press the power button to boot your machine. - Before the screen lights up (as soon as possible) hold down (opt + command + P + R) - Do NOT let go when you hear the chime! Your machine will act as if it is going to boot, you will hear the drive engage. KEEP the buttons held down. - You will then hear a second chime. Once you hear that chime you can let go of all of the...

You're going to need to run an SMC reset. Instructions can be found here

With the battery in, hover your cursor over the battery icon. Click on it (may be opt + click) ... it should give you a battery status in the drop down, and a link to explain the statuses. Depending on that battery status... you might have to replace the battery. If you've done an SMC and NAVRAM reset... and all connections are firmly reconnected then the problem you are experiencing is likely the battery. Quick questions: What was the reason for the GPU fix... i.e. Did you have a spill or a drop? Was the battery an issue prior to the logic board repair? During the logic board repair, did you make sure to shield the rest of the board from the heat? How long did the battery sit without being cycled while the machine was in need of / in repair? - After some time without power draining and charging, these batteries tend to go dead pretty easily. I had one do this to me after it sat for about a year, so I can't speak to any time frames shorter than that.

The first and most important thing here... Do no freak out. Don't jump to conclusions and all but ignore those that jump right to variations of "your logic board is fried" without knowing more behavior of your system than "It won't fully boot" First things first... you need to run some trouble shooting. Upon trying to start up, where in the process does it get? What do you see on screen? Is it making any noises: Hard drive engaging, fans, or is it producing any tones? If so what noises? If tones, how many... long short... is there a pattern? These tones are built in as error codes and can be helpful in diagnosing the issue. Remove the battery. Try booting from just the power cord. Results? - If the machine boots up without the battery in, then you will need to run an SMC Rest. This is easy, and can be easily accessed on the Apple Support pages. If the machine does not boot with just the power cable... again... where does it get in the boot up process? Will your machine boot into safe mode? (hold shift upon...

Have you booted your machine into Apple Hardware Test (AHT) mode? This will run a diagnostics test on your hardware (about how it sounds like it would from the name) and notify you of any errors. You can find out exactly how to do this for your machine here.

First try restarting the computer that uses this mouse. If it fails to start working: un-pair the connection... restart machine again... then repair the mouse with the computer. You should be good to go. If not, then you either need to check to see if you need to do any updates... Worst case scenario, the hardware in the mouse went bad. In which case you can either do a tear down and attempt repair... or search macsales.com or amazon for a replacement. With Black Friday around the corner deals are all over the place. I believe I saw one as cheap as $30. I'm not sure that it would pertain to this situation... If you want to try a SMC reset prior to a teardown or replacement... make sure that you have a backup of your drive and the data on it. Then do a search for " SMC reset" and the model of your Mac computer. Click on the link that leads you to the apple forums. There you will see a full example of how to do a SMC reset. Sometimes things like SMC resets and even PRAM resets tend to knock out any weird " t...

Shot in the dark (no pun intended in regards to your display)... Since you said that your SIL (Sleep Indicator Light) remains on, this is really only one of two things.. your GPU, which you've attempted to re-roll....or the display itself. From Apple Support, regarding the SIL behavior... " Startup When you press the power button to turn on the computer, the SIL will also turn on. As the computer starts up, the SIL stays on until the processor (GPU) has initialized and the display turns on. When the GPU initializes properly, the display will turn on and the SIL will turn off simultaneously. Running and display sleep While the computer is started and running, the SIL remains off. If the computer enters Display Sleep while running (the display turns off but the computer remains running), the SIL turns on and does not blink. It remains like this until the display turns back on, at which time the SIL turns off again. You can enable Display Sleep via Apple menu > System Preferences > Energy Saver, or by...

Mayer, as always, is on point. With the system booted, try following these directions: https://support.apple.com/en-us/HT201585 That should provide some detail to let you know if this is a battery issue, which is most likely. Also... much like the battery and alternator relationship in a car.... remove the batter and boot with just the power cable. If it works... and booting with the battery alone doesn't, it's likely the battery. Though, you're having intermittent issues, so I'm not sure if you would be able to get definite results.