Today as I sat down I bumped my computer as it was on, the keyboard and mouse didn't work, I cheacked all connections but it was just frozen, I tried turning it off with the normal front switch but it did nothing, I had to use the main switch at the back of the tower (pentium 3). When I turned it back on nothing appeared on the monitor and it just beeps for 1 secind takes about 2 second rest the beeps again, I opened it up to see if anything came loose but could not spot anything, what happened? How do I fix it? Any help would be appreciated.

Beeping is usually the motherboard error code.
If you have the motherboard manual you may be able to find out what the motherboard is "saying" which will point you in the right direction for fixing it.

Beeping is usually an error code yes, but in your case, because you bumped the tower, it probably means there is a loose bit of hardware on your motherboard, RAM is often the culprit. so give everything a check to see that it is in place and fixed in properly. hopefully this is all thats the matter =)