"strange ear-piercing beep come from the computer once every few minutes and last for about 5 seconds."
That's usually an OVERHEATING indicator. Try this. Remove the case cover and check that all fans are spinning and that no heatsinks are not clogged.
Leave the cover off till you sort out the heat issue.
I bought a VPR Matrix model 4100 computer (P4 2.53 processor, 100 gig hard drive, 512 MB DDR RAM, Geforce 2 32mb Nvidia graphics card) several years ago and have been having some problems with it recently.
It crashes a lot, often times randomly, and seems to max out the memory. Recently I reformatted the comp and installed Windows XP Prof. Edition with all the updates. When I tried to run Half-Life counterstrike the computer seemed to shut down (I could hear the familiar power-down sound), but the power light was on. After a while it turned itself back on again and when I re-entered the OS it gave me a flood of "Windows has recovered from a serious error" messages. The shut down seems to occur whenever I try to play a video file for too long.
I also here a strange ear-piercing beep come from the computer once every few minutes and last for about 5 seconds. I just checked out a book about upgrading and repairing PCs and hope it will help.
Could this be the graphics card, or maybe something wrong with the power supply or fan?