Cannot access BIOS

hello
System Windows 2000 Professional service pack 4
Home made computer AMD Duron 1100 cpu
KT7A Raid mother board
Problem is that last week the old cpu fried- heat sink was clogged by dust and the fan was very loud then packed up.
so I got a new heat sink and a 'used cpu' and fitted them. Th old cpu was an AMD athlon 1000 but as the new one is socket 462 it fits ok.
The computer started and ran ok, but on start said 'cpu unworkable or new chip'. So I went into BIOS and informed it that the chip was now 1100- rather than 1000. This seemed fine and worked. i was so pleased that I downloaded Advanced system care professional and paid for it. This did all sorts of whizzo things.
BUT next day I start up and the PC opens with a new desktop entirely. All my old icons have gone, my files have gone. Bizarre. I have not formatted the disk.
I cannot now get into BIOS. on pressing DEL on start up, the computer ignores me. Initially the keyboard mapping had changed too- I have moved that back to EN.
The machine 'works' fine, I get the internet ( obviously) but want my old files back.
Any ideas?
Sorry it is rather long- thanks for your patience.
( my wife says stop meddling- I call it mending!)

 

From one mender to another...
You could try removing the CMOS battery for a while to let it reset, then try again.

It also sounds like it might be opening into another user account. Possible? Go to the accounts list and see what's there.

 

Thanks for that, I did remove battery. I got into BIOS amended it back to old chip spec, but no change in set up od windows. It comes up as though it is a new install every time.
I used 'recuva' to find some files on C but some won't opne.
Also a USB stick I used for back up is now not recognised. Windows wants the drivers! GRRR
So I have a working computer but my work is not onit.
Frustrating .Under users I am listed , Administror and Guests.
Keep fiddling
Thanks