Computer keeps beeping! SOMEONE HELP!?!

I bought this computer from craigslist. Everything works fine (or thought it did) but when I run mutiple programs at once it starts beeping. Sometimes it will just beep for a second then stop then beep and so on. Other times it will just keep making a beeping sound and not stop until i close out some programs. I think the cpu is overclocked because its an AMD Phenom 2 x4 940 and its running at about 3.4 ghz. Everywhere i have looked says they run at 3.0ghz. So the only thing i came up with is that its running to hot. If that is the problem then how do i set the cpu back to stock settings? Also it has 2 western digital caviar green 640gb hard drives in raid-0. I have read in a few forums that you shouldnt run the caviar greens in raid-0. If this is the problem then how would i fix it?

I know the basics on building computers but when it comes to overclocking i have no clue. Also whats a good program/software that i can get to see what temps my computer componets are running at? Thanks for all and any help you can give me!

Computer specs...
Gigabyte GA-MA75GM-S2H, AMD Phenom 2 x4 940, XFX radeon HD 4870 1gb, ocz reaper (2x2gb) 1066, 2 WD caviar green in raid-0

remove ur memory and clean it,reset cmos battery!