Before taking the system into a repair shop, if you feel comfortable opening your system case, do so with the power turned off and power cable unplugged from wall. (most newer systems will supply power to the motherboard while the system is shut down.) Ground yourself (preferably with a grounding strap). Remove and then reseat all add in cards in the computer. Then remove and reinsert each memory card.
Through use and the process of heating and cooling cycles, or moving the computer from point A to B, a card can become partially disloged.
Depending on the number and sequence of long and short beeps, you can determine with a manufacturer's chart what component is bad. Beeps commonly are caused by memory chips or video cards bad or unplugged.