Sometimes my pc will boot and launch Windows fine, other times, it will go to a black screen asking for a boot disk. It flashes the Windows XP loading screen first before the error. Other times, after it's booted correctly, it will just go to the black screen. I took it to someone to fix, and it never did it for them. They left it on for 3 days. However, a few hours after I got it home and running, it went to the boot disk screen? Any suggesstions?