It doesn't seem likely, but beeps from a Dell computer can be bad memory chips. You can try removing one or more to see if the beeping continues. Dell memory specifications for this system are quite restricted, PC2-5300 and PC2-6400.
Another possibility for a beep include a bad CMOS battery. The CMOS battery helps the computer remember various settings including time and date. If the system cannot recognize the date in the CMOS memory, it will complain.
There are other reasons for the beeps, but I do not have a list off the top of my head.