My bets are ram or video card overheating/video ram itself.
Can you open the case and remove the video card to see how much dust is in the video card? if there is allot clean it out with compressed air(you can get a can at any local computer or even automotive store...)
If you are familiar with how to remove your ram, take it out and put it back in(sometimes it can come loose and may in rare cases cause video corruption).
Once this is done, try to get into windows...
If you keep getting it your video card's ram may be toast. If you have access to another video card(Borrow one from a friend) try that and see if the problem goes away....
If your blue screen message auto reset the system try the following to make it stay up until you hit reset, If its already like that, skip this part
Once in Right click on My Computer then Properties.
Select the last tab(Advanced)
Under Startup and Recovery click on Settings
About half way down the window it open remove the checkmark from Automatically Restart.
This will allow you to see whats on your blue screen.....this is provided the corruption will let you see it at all
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In order to help you better, try to gather all the info you can about your system
CPU
Motherboard
Memory
Video Card
Hard Drive
Power Supply
Ect