Hp DC7700 SFF Desktop Random Beeps and Booting Issues

I have an HP DC7700 Small Form factor Desktop PC. it has 6gb memory, and running and Intel core 2 duo 2.4 ghz CPU. It started by giving me a beep code of 2 beeps and a pause and repeating 2 beeps. I’ve changed the power supply, I re-seated the memory which it then gave me 5 beeps on repeat. I’ve reset the cmos, changed the cmos battery. where it proceeded to give me 9 beeps on repeat. It will started up after pressing the power button anywhere from 3 times or more. Once booted it works well. but if I turn it off and leave it for more than half an hour it starts over with the beeping and won’t boot again. Any ideas?