those beeps are commonly caused by (and lets hope it's caused by) one of the following problems:
*one of your Mobos various connectors is loose/dicsonnected (ie: usb header, pci card, etc.) just check all of your connections and push in anything that looks loose (use your mobo manual to make sure you've covered all of the connections)
*your CMOS button cell battery (on the MOBO) is dead/fallen out and needs replacing. check your mobo manual for specifically what kind of battery you need. find some one who sells that battery, buy it and pop it in.
more severe/pricy-to-fix problems include:
*you HDD is shot, you need a new one. it is still possible to recover the lost files using various methods described by various internet sites.
*your power supply in inadequate/broken and needs replacing.
NOTE: if you shut off/unplug your power supply to check internal connections, wait about 30 seconds after turing the power supply back on before you boot up to allow the mobo to rcharge or you will get that same beeping. When you restart your comp after a beeping fit, you may get a CPU speed error message. this is usually caused by the cpu trying to start but it didn't have enough power. that error message will let you know with more (but still not complete) certainty that your power supply is failing.
good luck, and if you have more questions i'll check up on this thread occasionally for a couple days