Why Is My Mac Beeping During Startup?
If your Mac is beeping once every five seconds that indicates that no RAM is installed in your machine. This is common if you have just attempted to install new RAM. Your best bet is to remove the RAM and reinstall it. If it still doesn't work your RAM may be bad.
If there are three beeps and then a five second pause before three beeps again, then your RAM is not passing a data integrity check. We advise taking your Mac to the Apple Store Genius Bar.