Very grateful for the replies here and I have taken immediate steps to copy my hard drive just in case - something I do occasionally.
Much troubles. Maybe started a couple of weeks ago when my VPN failed to load. While struggling with this and finding that I could get it to start by first using Tweaking tray icon - 'clean memory' but something was locking the CPU at 100%, another clean memory brought the CPU back to normal, a number of other problems started occurring:
On my desk top I clicked on 'Spybot' but it failed to open. Rebooting (Tweaking style), I was clicking F8 to do full Tweaking but it just carried on to boot normally. Tweaking tray icon loads on booting so I looked for boot to safe mode but it was missing.
Anyhow, I clicked 'Spybot' again and the recycle bin opened, on impulse I deleted the spybot icon but of course only succeeded in deleting the recycle bin.
Spybot and its immunisation feature have been useful in (temporarily) removing another annoyance and that is an apparent 'stuck key' fault giving /////////// or 999999999 in menu boxes and then scrolling failed in that it would fight (and win) to stay at the top of a page. I loaded Tweaking and the update came up which then gave me the MD4 nonsense.
Since my posting here I have deleted Tweaking, Spybot and the VPN and reloaded them but with the previous version of Tweaking.
From tweaking I did a reboot to safe mode as my F8 command still does not function. The computer restarted with wild beeping for several minutes before the loggin page appeared but the loggin box was flashing in and out in a fragmented style. after a few more minutes it settled to 'wrong password' and I could proceed from there. However it was still a normal boot up.
To get safe mode I had to cut power to the computer. Not something that I wanted to do but it gives immediate safe mode on starting. Tweaking and Spybot scan have brought everything back to more or less normal. I still get 9999 occasionally but Spybot repairs it. VPN wont load automatically but it does manually.
The worst part is that Tweaking is not fully functional - in Step 3, I went straight to a check disc reboot, it managed this after all the beeping and flashing again, only to get the messages check disc scheduled, check disc cancelled.
Another power cut reboot and this time I went for the simple check and surprisingly, all was well.
Step 4 said that there was a repair scheduled that required a restart so could not proceed. Clearly that was wrong so I moved on to repairs.
Computer will shut down and and start as separate actions but restarts provoke the mad beeping frenzies.
I am still looking at the detailed guidance so kindly given by Shane but I have had enough for the moment and I am pleased that I managed to resist picking up that big hammer in my workshop.
Thanks all,
Jamest.