Hi I purchased a used Optiplex XE2. It worked very well for a short while, but now it won't start. The power supply is delivering all specified voltages, but when I power ON, I get a single beep tone every five (measured) seconds and the Power LED and the HDD LED comes ON for about half a second, then the Power LED goes to orange, then the cycle repeats. I am guessing it is not getting to the POST stage. Any suggestions welcome please.

Service tag

Cheers Ken