Hi,
What is the full model number of the desktop?
Have you re inserted the RAM module (memory stick), you didn't say?
Having no RAM module inserted will give a 5 power light blink, 5 beep error code
If you have re-inserted the module and are still getting the error light/beeps, replace the module with a compatible replacement module and check if this resolves the problem.
If it still fails it may be a memory controller issue on the motherboard