For what it's worth.....
I ended up sacrificing the recovery partition and chose to bypass the entire RAID configuration thinking that was the ultimate source of my problems. Made the necessary changes in the RAID controller setup and in CMOS to configure the two 500GB drives independently as C: and D:. I did not like the reinstall process from the system recovery CD/DVD's as it was difficult to pinpoint all the specific drivers, system apps, etc. So I decided to revert back to the original config from the factory.
I re-enabled RAID0 by reversing the steps mentioned above and did a full system restore from a system image I had done earlier before all the problems began. The restore process repartitioned the two 500GB drives as one C: along with the 15GB recovery partition D:.
I did this last weekend and since then have been installing one application at a time and the system has been very stable. No unexpected shutdowns or errors on the RAID startup screen when booting. It seems logical that the unexpected shutdowns more than likely corrupt the RAID setup; thus one causes the other.
I'm hoping that rebuilding the system may have resolved my issues. Time will tell.
Unfortunately the engineer installed the drives as RAID 0! So I ended up deleting that array, putting one of the original drives back in (which they have left us with for a few days to make sure all is OK) together with one of the new drives - this was added to the original RAID 1 array, courtesy of the original Samsung drive and the Array rebuilt itself. I then swapped the original Samsung for the other new Seagate Barracuda and this was added to the array which is currently re-building as I type this, so I have got the original data but on an array with 2 new drives, took a bit of time, but was less painful than re-installing everything again!
Be interested to know if other people who have been affected by this also have Samsung drives - which is what Dell claims the problem to be...