PC wont boot with any drives attached, drives are fine

I have looked on google and this fourm but havn't been able to find anything that fits my situation. I am knew on here but have read many posts on here before and fixed problems before. Let me know if I have missed something out i've tried to cover everything.

I have had my system running for almost a year but about 2 weeks ago it wouldn't post I replaced the hard drive with a brand new SSD and a fresh install of windows 7 so I cant have two hard drives with the same problem? so the new drive fixed the problem until now 2 weeks later I'm stuck again with the same problem. if I view the post messages it gets stuck on auto-detecting hard drives. If i take all my drives out including dvd it will post and ask for boot media.

I was thinking that is either a memory or motherboard problem.


system:

motherboard- ASUS M5a78l-M
cpu- AMD FX4170 @ 4.2ghz
memory- 1x 4GB corsair value
PSU- ACE 750w
HDD- seagate 1tb
SSD- OCZ 120gb
Graphics- nvidia gtx 660Ti
DVD writer- LG


Really apreciate any help, Thanks in advance,
James