Blue screen error

Hi there, im having this problem fixing a friends old laptop.
Aparently his ram wasnt working properly and the internal motherboard battery was failing as well and wouldent keep the bios settings.
So, i replaced the damaged ram, changed the battery on the motherboard. Then when i booted the laptop it would come to the part were it asks yo if you want to start windows nomaly or in safe mode etc. so i would select any of these options and the screen blinks and for just a split second a blue screen apears and it restarts again, theres not enough time to make out what the error on the blue screen is.
So then, i took out the hard drive and reinstalled windows with another laptop, and changed to a different ram as well just in case. And to no avail, it always does the same thing and wont start up.
I tryed changing some options in the bios, but dosent really do any diference.
So if some one could help me out with this one, im really out of ideas to as what could be causing the error.

If you need any more details ill be happy to give them.