Your problem is going to be one of four things.
First of all check to see how hot your cpu is running when in windows.
If that checks out ok and the temps are not high well knock that off the list.
You want to be looking at errors on your hard disk drive next, so do a scan disk of it to see if you get any errors.
The next thing to check is your system memory.
You can do both of the steps above by using your windows 7 OS install Dvd by going to the repair tools option when booting the disk.
Now if all of these steps report everything is ok without any errors on the hard drive or with your memory.
You need to consider that the problem may be down to a bad power supply in the system, that is becoming unstable causing the errors you...