A 'series of beeps' is almost always memory related, but it might be a hard drive that is not working properly.
Did you upgrade the memory? You can try reseating the memory - that may help. That's really the only thing you can do yourself.
Try testing your iMac with the Hardware Test. Insert your restore DVD disk #1, and reboot while holding the D key. Run both the normal test, and the extended test. Call Apple, and tell them what errors you see in that test.