It could be several problems.
First I would re-seat the video card, and re-seat the RAM. Make sure everything is snug. If not then I would check the power supply, ensure it is outputting the proper wattage.
If you look up your motherboard's instruction manual, it will tell you what 5 beeps mean
For instance, an AMI motherboard, 5 beeps means: Your motherboard is complaining. Try reseating the memory and rebooting. If that doesn't help, you should consider another motherboard.
** Edit ** It could also be indicating that the CPU has failed. If you have checked all the above, then most likely the CPU has failed. Perhaps it was overheated or something. If you are going to replace the CPU, might as well upgrade the motherboard as well
