Keep getting messages from "MS Removal Tool" telling me my computer is infected & when I followed it through, it wanted payment (in USD) but if I try to close it down, I get thrown into a loop - is this a legitimate MS thing - or has something wierd happened to my computer ?
Download, install and run the free version of Malwarebyte's Anti-Malware. It will get rid of the malware which has found its way onto your computer:
http://www.malwarebytes.org/mbam.php
MS Removal Tool or also called as Microsoft Removal Tool is a dangerous fake security application that entice computer users to do actions that will benefit the developer of the rogue software and pay for it via online transaction. MS Removal Tool virus will come bundled with executable files that can be downloaded from a file-sharing network. Fake online virus scanner is also another means of spreading MS Removal Tool virus. These web sites will run a full scan on visitors computer and provide believable results stating that PC is infected with various threats.
Then go with Buenchico's suggestion. all the best!
If you can't get Malwarebyte's Anti-Malware to do its job while your PC is in 'normal' mode, boot into Safe Mode. (Hold down F8 while starting your computer). The display will look weird (because your video driver won't have been loaded) but you'll still be able to run the program you require.