OK, so after completing the steps, I was unable to get the machine working: A new error appeared about diskette 0 not being found and I was unable to invoke the boot menu, and despite the CMOS battery being in place, it had a low voltage warning.
Also, I am still unable to get into the BIOS.
A few more reboots and I was able to get into the boot menu, although I am still having to let it go to the diskette missing page, and then press F1 to continue which then gets me back to boot menu.
This is a bit worse then when it was, although I can still boot windows via the boot menu. The diskette issue is something I need to live with. There is nothing attached to diskette 0, but obviously I can't disable the channel in the BIOS setup.
So I'm out of ideas. I'm toying with the idea of getting a new mobo, but it's not like the machine doesn't work.
In better news I managed to fix my Mother In Law's Toshiba C660-220 laptop last night! Cost the price of a new HD and downloading/burning of Windows disc, but it works.
(If anyone is reading this via a search result, the symptom was a black screen with mouse pointer / cursor after the windows splash screen. USB mouse was also not working. This was also happening when I tried a new windows install. Removing the HD meant I could start the install process and use a USB mouse, but obviously with no HD installed I couldn't continue, so I installed a new HD and hey presto, I was able to install Windows 7 Home Premium again. It took me a while to find the correct WLAN driver...if you need this, contact me here.)
Now I just need to RMA a faulty WD drive that was the whole reason I wanted to check the BIOS on the E521....
Thanks again for all your help
Edited by nextx, 26 March 2015 - 04:45 AM.