Is your keyboard and mouse USB or PS2?
So you turn on the computer, and it just beeps. What do you see on your screen? Are you able to start-up with a boot disk? Try unplugging anything that is USB and use a boot disk to see if you can start-up. Make sure the network adapter is unplugged.
When you try to start the computer and it beeps continuously and nothing appears on the screen, some or all of your RAM may be bad. This is the most common cause for this type of problem.
Pull your RAM out and reseat it back in the slots. Attempt to start up the computer a few times, if it starts up EVERY time you start the computer then you may be alright. If this doesn't help then if at all possible replace the RAM inside of the computer with other RAM you have around (make sure it is the right type of RAM that will work in your system first). Once the RAM is replaced, attempt to start up the computer a few times, if it starts up EVERY time you start the computer then you have more than likely found the problem. Now all you need to do is buy new RAM (making sure it is of the right type for your computer).
I've never seen this happen from what you have described, but in my experience if the computer is just beeping at you then RAM is the usual suspect. It's possible a power surge would burn out your memory....just an idea.