Computer Won't turn on, only beeps.

I have a Inspiron 560 from probably 6 years ago now and at one point it wouldn't turn on. At that time when i did try to turn it on my computer monitor wouldn't do anything and my desktop would only beep at me. I ended up frustrated and just gave up after a half hour then the next day tried to turn it on again and what did you know it worked. Thinking nothing of it I just continued on. The other day it did it again. Frustrated for a second time i open the computer to make sure all the drives and disks and what not where firmly in place and everything seemed fine. The # of beeps were inconsistent. At one point it would make 2 or 3 beeps and when I would mess around with the inside of it trying to fix it the # would change. Finally it settled on 6 quick short beeps. Today out of desperation i turned it on one final time and Wa La it works. So now I'm just curious what's going on with my computer. Each time the monitor does nothing, the tower just beeps at me.