Knowing a bit more about the computer and problem would help. Could you give us some specs on the machine. Motherboard make/model. When the problem occured. What (if anything) you did before the problem started. Has it worked before?
General stuff to try... Remove anything removable (well, CPU could probably stay if you haven't messed with it recently and it worked in the past) and try it with as little as possible (CPU, single stick of RAM, maybe video) See if it continues to act up, if you get the no video beep (1 long 2 short), etc etc.