6 beeps on Dell optiplex gx270

Possibly faulty RAM which needs replacing. To confirm, test with Memtest86 bootable CD.
Download the CD ISO from here: http://www.memtest.org/
Create CD from the ISO using IMGBurn: http://www.filehippo.com/download_imgburn/

Boot your Dell from that CD and Memtest86 will start automatically.
It will continue to run indefinitely until you press the <Escape) key.
Any memory errors will usually be flagged up within the first 4 passes, at which point there's no need to continue with the test, just replace the RAM.