Why does the screen boot so slow

I would check the SMART status of the hard drive. If it has bad sectors, it could take a long time to boot into Windows, making you think there's a fault with the screen. An easy program to check the SMART status is Crystal Disk Info. If it's anything other than blue, I consider replacing the drive and installing the OS. If you have a linux boot disk, the disk utility in Ubuntu or Mint will tell you if you have any bad sectors and you'll see if it goes through POST and boots into the OS in a faster manner.

I have seen this problem, the screen is black and you can open Task Manager to do some things. This is a profile issue, try signing in as administrator. If you don't know the password, you can use Task Manager to open Computer Management, click on Local Users and Groups, then click on Users and right click on the administrator account and choose set password, set the password. Log out and then try signing in as Other User, use the administrator account and password. If the administrator account works correctly, try renaming your account so that the OS is forced to create a new account for you. If that all works then you can transfer your data (desktop, Favorites, Downloads, Documents) to the new account. Be sure to make the new account an administrator. Good luck.