Hmmm Not sure how much more effort I can put into this. The irony is that I'm planning to order a new tower PC in the next month or so. Maybe I'll just format the drive and install Ubuntu and use it as a spare machine. I don't have any real understanding of just how far-reaching this problem will be. Ubuntu is fine running off the cd, but if I do a full install will that then get sidelined by the BIOS problem?
I have no idea about BIOS issues. If I could manage to do an upgrade of the BIOS, would that fix the issue or is that an each way bet?
Addendum:
OK, it's fixed!!!!
Why the BIOS should suddenly not recognise the HD is a mystery since there is clearly nothing wrong with the drive. This was not the initial problem actually since the problem started out with a Windows Boot Manager screen saying Windows failed to start.
At some stage, this became a "Disk Read Error" message on boot up.
Anyway today I ran TestDisk again. Had previously run it under Ubuntu and recovered something or other so that the partitions showed properly but it still would not boot. Anyway this time on rebooting I got back the Boot Manager screen saying Windows failed to start. This time I went through to the Windows recovery disk and after about 6 reboots the Vista installation is working perfectly again. How flaky is that? I still feel like either easyBCD or a Partition Manager caused the problem. I freely admit it may have been finger trouble, but I'm a bit aggrieved it was so difficult to get it working again. It's taken a week working at it at least half of every day if not more!
Thanks to whoever recommended TestDisk, or maybe I just found it on another forum or thread? Thanks for all the ideas anyway. I'd never have got there without all the nudging along. Hope this helps someone else.