Damn, that reminds me the old days...
Back in 2004, I bought a computer with, if I recall correctly, an ASUS P4P800-E Deluxe, P4 Prescott 3.2Ghz, 2Gb Corsair Ram and some random 200gb HDD.
I had the same problem, at some random time, my computer would tell me "no bootable device insert boot disk and press any key". After, like, 4 or 5 windows reinstallation, I decided to get a new... motherboard...
Problem solved...
Have you try your SSD on another computer ?