But I put the ram into a EXACT same modle computer and it worked. But i mergedt the ram with some already. (512 to 1GB)
That could be your problem right there. If you're using multiple different RAM modules, one of them might be conflicting with the other OR one of the RAM modules is not compatible with the DIMM you're using it on (i.e. a 1333 Bus RAM module on a 800Bus board).
If the problem started after installing this other RAM module, then I suggest using one module at a time. If that, the incompatible RAM may have damaged the board.
Second possibility could be a worn out CMOS battery. Try replacing that and loading Fail-Safe defaults into the BIOS and try booting up again.
The POST beeps are indicative of an obvious hardware failure; however, seeing that it's random (or "every now and then") it'll be necessary to know what kind of BIOS you have as POST beeps vary. Some newer mother boards have actually done away with the beeping and replaced them with LEDs.
Once you're aware of your BIOS version, check
www.computerhope.com/beep.htm for a list of Beep causes and solutions.