Windows not starting sometimes

When I turn on my PC or restart it, it sits there on a black screen with the "_" blinking in the very upper left corner. And about 5-10 minutes later it tells that the disk boot failed or something and that i need to insert a disc.

I have my recovery discs which I have used before to restore my PC its original factory condition (two times before today). I usually do it just to get a fresh start with my computer after having quite a bit of games and such installed.

So I did a total of 3 factory condition restores and I still get the problem. Sometimes windows starts up with no other problems. I have the feeling that its only going to get worse and it will start to never work. Is there anything I can do?

If it matters heres a few of my specs(may not be all the of the correct terms):
windows vista 32bit
amd dual core processor
3GM ram
two 288GB harddrives
nVidia Geforce 9800GT overcloaked


thank you in advance