Normally 1 long Beep is a RAM issue which could be anything from a Faulty Module to a Timing Mismatch between 2 different Modules.
The way to proceed here is to test the RAM with something like Meatiest on the Ultimate Boot CD ISO available free here
http://www.ultimatebootcd.com/download.htmlThen burn to a CD and set your BIOS to boot from the Optical Drive before the HDD and Test the RAM.
I would also suggest looking at the Data & Time on the First BIOS Screen to make sure that they are correct because the wrong Date can play havoc with Computers. That quite often happens when the BIOS Battery goes flat and the Real Time Clock looses power.
The Ultimate Boot CD is a full set of Diagnostic Tools to test the Hardware with so if the RAM Passes you can test the remainder of the hardware including the CPU with several different tests.
Col
