Lenovo G475 won't boot unless I wait several hours


Jan 17, 2016
I have an old Lenovo G475 with a broken screen connected to a TV that I use for Netflix, emulators, etc.
The problem is that, whenever I turn it on, it behaves super weird:

-If I wait seconds after turning it off, it doesn't boot and tells me that there's a file that doesn't match with checksum or something (can't even enter BIOS).
-If I wait some minutes after turning it off, it tries to run Windows but then crashes and gives me a BSOD (now I can enter the BIOS). Sometimes it let's me choose if I want to start windows in safe mode, but if I do, the upper half of the screen goes white with weird graphical artifacts.
-If I wait an hour, Windows finally runs, but only lasts for a couple of minutes and then crashes again.
-If I wait a day, Windows runs normaly for about an hour, and then crashes.

I was thinking that it might have something to do with the BIOS, so I want to flash it, but i'm afraid it'll crash mid-flash.

(Sorry for my english!)