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Long story short, I fried up my nVIDIA video card on the Lenovo ThinkPad T520 and did a stupid setting in BIOS to force to use that video card. Without surprise the screen is black when I boot the laptop though it still have a fully functional HD4000. So the question is: is there any way to reset the BIOS physically without changing the chip so that the config for display will go back to use optimus by default? Or any other idea helping me out is welcomed.

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up vote 2 down vote accepted

To reset your BIOS:

  1. remove your battery
  2. remove any AC adapters
  3. hold the power button for 1 minute
  4. install battery and AC adapter

    Another way is to unplug your CMOS battery... (a lot more work involved)

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I tried (actually I tried tear off the CMOS battery too). The BIOS seems to be reseted so I will accept this answer. However, when restarting it now gives out beep and decoded as system board fault. Any idea on that? Thanks. – YankeeWhiskey Apr 6 '13 at 2:20
the boot / bios error is caused by your dead GPU, i don't see anyway of getting rid of the error without soldiering another GPU to your Motherboard. – dashboard Apr 6 '13 at 2:22
I also am stuck with "use discrete graphics" BIOS option and desperately looking to hard reset the BIOS settings. My T420 doesn't even display any POST messages and keeps restarting itself in an infinite loop. I performed the procedure described above in addition to disconnecting the CMOS battery but nothing so far. Any ideas? – Aamir Jan 15 '14 at 5:15

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