Thanks for your input Charles (Ascot).
The RAID configuration is supposed to be 0 - however, before this 'problem' with booting the old PC up, when accessing via the 'This PC' icon to see the drives etc., only one of the hard drives showed populated with info - the other had lots of free space. I don't understand RAID myself either but always expected it to be one drive mirrored the other - in which case they should be showing the same
Answers to your questions raised.
I can't access the Vista system for a long enough period to gain the access I need. At boot up the machine will show a message about 'floppy drive boot' not available... or something like that - and the screen goes black and the 'beep' starts. I then have to re-boot and enter the BIOS to set the boot type and RAID configuration. It will then boot up 'sometimes' but, like I said, not for long enough. If I access the mail program it sorted of crashes... not good.
I removed these two 500GB drives and tried each in an external caddy. plugged in the mains cable to power the caddy and connected via USB to a Win. 10, i7 32GB laptop and switched the caddy on. The laptop will 'find' the drive and list it (via the 'This PC' icon window) as drive F:/ but when trying to open it I get the messages I mention in the first posting.
I wasn't sure if there is a setting in 'device management' or similar but I've not had any success yet in finding it. It would be nice to be able to go through the drives and find stuff that I have forgotten about or have used and don't want to loose. It's now about 6 - 7 years old. Ho hum!
With the 'beep' and also the black screen on an initial boot I did wonder if it was possibly something to do with the 'heat sink' for the processor... I've also wondered if the on board battery was not holding charge which was/is causing the machine to not hold the boot up info in the BIOS and hence why I get the message about a floppy drive?