No Display, No BIOS got messed up trying to install linux with win 10

Hi Guys,

Let me better describe the situation here. It's an old dell inspiron 15 7537. The hinge of the display was broken long time ago, so i removed it and was happily using it as a dekstop with external monitor, keyboard and a mouse.

As the disaply was removed it use to beep everytime it starts, but everything was fine and i was running windows 10 with secure boot option i think.

One fine day i decided to install linux mint along side with the win 10 using a pen drive and totally messed up i guess with UEFI and legacy mode confusion.

Now all i wanted to access is the BIOS so i can use a pendrive to boot and install either linux or windows from sratch as data in hdd is not a concern for me.

Tried below:

1. Removed CMOS battery for few min put it back and turn on.
2. Removed CMOS battery and turn on.
3. Removed battery and hdd and tried directly with dc power.
4. Keeping power button pressed for long time.

All the scenario result in same that is when i press a power button all lights trun on including cpu and hdd , cpu fan starts spinning with beep, but there is no signal to my monitor and pressing F2 or F10 simply reboots the device.

Any help is appreciated.