Freezing then Issues on Start up

I have been having issues with my PC freezing. I just started using Windows 7 after my PC crashed couple weeks ago. I upgraded from Vista 64 bit.
Since then it has been fine except the PC freezes when I play Starcraft 2. I can play the game for about five minutes or so, sometimes more/less it just depends, then it will freeze, the music/sounds that was playing at the time of freeze keeps replaying, and I have to manual reboot.

After I manual reboot when this happens, I get weird issues on start up. Sometimes it will say "failed to read boot disc" or "fail to start windows" "press ctrl+alt+delete to restart". Sometimes it will run CHKDSK on restart and this morning it ran Windows Repair and determined the problem could not be fixed and windows couldn't be started. I turned the PC on and off right after it told me that and it worked fine.

This is very strange to me as I never had any issues with the game freezing on Vista.

System Specs:
Intel E8400
Nvidia GTX 260
4GB Ram
Win7 64 bit
Biostar motherboard (all I know about it)

I have unistalled and reinstalled the game, along with the video card drivers.

Any help is greatly appreciated, thanks!

Thanks for the reply
But I am not sure how that would help because it start up problems happen randomly after a freeze. Sometimes it won't happen and sometimes it will.

For instance here is my experience this morning.

I ran Windows Memory Diagnostic this morning to see if I had a RAM problem. The first time I ran Windows Memory Diagnostic, I checked on it after a while and my computer was a black screen. I hit CTRL+ALT+DELETE and it restarted but gave me no test results. I re-ran the test and it came back with no problems found. But soon after that my PC froze while writing an email, and when I tried to reboot I got "Can not read disc, press ctrl+alt+delete to restart". I left the PC off for 30 mins and tried again and it has started fine. Every now and then it will act slow. Do you think I might have a RAM problem although the test came back good?

I opened the command prompt and typed "chkdsk /v" and all I get back is "Access denied you do not have sufficient privileges. You have to evoke this utility in elevated mode".

I am not sure what to do

Ok thanks for the help so far.

I ran chkdsk /v and got "no problems found"
I also restarted and ran chkdsk /r, and I looked at the event viewer but am not sure what I need to be looking for.

On memtest86, I downloaded the file, but am confused on how to use it. Do I need to download an ISO burner program and put the unzipped file on a disc, or do I need to unzip the files, then use the ISO burner to put them on the disc?

Because your getting intermittent disk boot errors it suggests the HDD could have an issue. Try reseating the cable and see if that helps! A HDD test would bew useful about now but if im honest, im not sure of the best ones around so it maybe worth waiting to see if someone can suggest a decent one to give good trusted results! :)

I ran memtest86 over night for almost 9 hours, when I woke up it said Pass:7 Errors:0
So I guess its not a ram problem. What do you suggest I do now?