it's not the PSU, swopped in a 1000W COrsair, RM1000X, been thinking of doing that for a while anyway.
now got 1 stick of RAM, Asus board, 3770 cpu at stock, one corsair SSD. Froze after about 5 mins. CPU in bios showing 33C under stock cooler. I'll build it back up and see where it jams.