COMPUTER WOES :-(

Oh why oh why....

So it was the modem the other day and today, I am afraid that the motherboard may be going south. Since I am not a hardware person at all and somewhat despise it, I am looking to my dear friends who love building their own computers and such for some advice and opinions.

Current Issue:
-Turn on the computer and monitor
-Monitor has screen that says the monitor is working check the cable or pc. (this has happened twice prior to today. Then today it happened 3-5 boots.)
-Tonight I realized that the mouse and keyboard also were not functioning while receiving this screen on the monitor. (Assume that was probably the case all along because I had to hard reboot the pc each time)
-The 2nd boot this morning resulted in the keyboard functioning and the monitoring scrolling lines up and down. I was able to login and reboot by knowledge of the process.
-5th bood, Kwadwo suggested unplugging everything from the pc and plugging it back in. I did and the computer rebooted and everything is currently working.

I fear turning it off because I am afraid it will not come back.

** Any clues what might be the issue?
The computer will be 4 years old in Oct. The harddrive is about 2 years old. Monitor is probably more like 8 years old. Mouse is fairly new. Keyboard...hmmm not sure which iteration this is, but probably around 3 years.

** Suggestions on fixing the issue?
Wasnt really looking to purchase a new computer anytime soon. This one suffices for what I need, it even has a DVD player in it. The only reason it doesnt have XP is because I didn't want it. Its a Windows 2000 box.

Thanks for all the advice and suggestions.