Computer won't boot all the way

[Skandaluz]

Hi guys, I have this little problem that's been bothering me for a while now as I can't really find out what's exactly wrong. Here's the problem:

For a while now, my parents computer has been acting weird when starting it up. After you turn the system on, it sometimes loads and boots to windows just fine and dandy, no problems at all but the other half of the time when the computer is turned on, right after the windows loading screen (the scrolling bar thing), it'll just stop right after the loading screen and just have a blank screen where as when the system does boots all the way, the screen will blank out after the loading screen and then display the windows log in screen.

Here's what i've tried so far:
-Swapped motherboards w/ a new one (worked for a while but problem still came back)
-Swapped ram (same problem)
-Swapped hard drive (same thing)
-Swapped processor (same)
-Swapped power supply (I came to think that maybe it's not getting enough power or such so I swapped the power supply but the problem still persisted.

Anyone know what may be the problem?

TIA

 

[jackschmittusa]

Driver issue?

 

[Skandaluz]

I had thought about it but I've used two different video cards but the same issue still persisted.

 

[robisbell]

if you can get it logged in fine go to http://housecall.trendmicro.com and have it scan the hdd's completely, all files and folders.
report back the results.