OK, fixed it, thanks to related posts on associated BIOS flashing tricks.
The Strontium 1600 RAM seems to be causing the issue.
FIX: After removing all case connectors, putting in A-DATA 4GB 1333 RAM, with FX cpu installed and successful BIOS update checked, the 'clear CMOS' pins are shorted with a screwdriver. Box restarted, fans all roaring at max, no POST. Turn power off, short 'clear CMOS' pins again and restart. Now fans go quietly and box boots to POST, shows message 'load last good BIOS setting?' press enter and it boots and runs win 7 OK.
Remove A-DATA 1333 stick and replace with 4GB Strontium 1600, no POST again. Put A-DATA 1333 back in, POST ok.
The site below says it is compatible with both types.http://processors.findthebest.com/q/867/5445/What-kind-of-RAM-is-compatible-with-the-AMD-FX-4130-processor