Well i ran the xp cd and tried fixboot, fixmbr, bootcfg rebuild and finally chkdsk. The first three had no effect, chkdsk helpfully told me there was one or more unrecoverable errors
. Sounds more hardware than software to me even tho an old maxblast disk checker (and "smart") say its ok. I put the drive in a caddy and managed to get off important files with no bother. I also tried an old drive in the broken pc and it worked, so the problem is not mobo/ram/psu or bios related. My next plan is to try an XP repair install, failing that a format and reinstall and failing that i'll RMA the drive and get a new pc...unless anyone has any more suggestions ?