The single beep sound mean u have pass POST (Power On Self Test). Various beep sound means different problem.
No beep sound is the worst problem. U have FAILED POST. Likely your processor or the mobo is fried.
Had a similar problem b4, thought it was mobo. Changed and still the same, finally changed processor and sloved the problem.
Quite diff to test, it could the mobo that fried the processor, unless u have a spare old processor that u don't mind get fried.
A quick way to test if it's the RAM problem. Plug out the RAM and boot the system. If still no beep at all, then it's not the RAM problem. RAM problem will give u a few beep sounds depending on the bios.