The Registry Cleaner I used is called "Remove Tuneup Utilities 2014. It was installed accidentally when trying to install "Advanced Uninstaller PRO 11" which someone on a different forum (TalkGraphics) recommended being as it manages to remove crud from your registry that it seems almost every program leaves behind when being uninstalled.
I shall now go ahead and reboot into Safe Mode with networking and do as you suggestion Layback. More shortly.
EDIT01
Not looking good. The window that pops up when you first log in using "F8/Safe Mode with networking" is freezing on the screen. Cntl/Alt/Delete task manager says it is not responding.
...And now I cant get any of my browsers to open.
...Gads and now I'm finding it hard to reboot from even from Safe Mode.
EDIT02
Okay I have rebooted back into Safe Mode. The reboot too rather a long time (about 3 mins?). And then I couldn't open a browser. So I am attempting to reboot again
EDIT03
Tricky. It has rebooted (v slowly) back to that window in Safe Mode called "Windows Help and Support", except that the window is all white with no text in it - I.e. it has screen has seized up.
When I hit Control/Alt/Delete it's clear that that area of the screen has seized up as ONLY that area of the screen changes colour. Also, within Windows Task Manager > Applications it says "Windows Help and Support" - "Not responding".
I am now wondering if I should reinstall window from scratch? And if so whether I would be better off upgrading to Windows 8.??
I do still have my Windows 7 x64 original CD etc. However re-installing Windows would lose me about 3 or 4 days of my life !!
I think I also have a Macrium Reflect Free rescue CD (from about 18 months ago)...
EDIT04
I did manage to run a copy of RKILL which I had previously downloaded, but I can't get any browsers to open.
EDIT05
This is hopeless. I am now trying to re-boot of a Windows Repair CD.
EDIT06
OK I ran a microsoft hardware check but it seemed be okay. (Although I'm not 100% sure because I never saw any final report)
EDIT08
I managed to download Microsoft Security Essential onto a different PC and copy it over. I then managed to install MSE. However it seized up during the update. [grrr]