**UPDATE** Now sorted thanks to ALT key enabling me to navigate reasonably well***
First whiff of somethig up was I did not need to click on my account name when XP Pro had booted. Now the PC is unmanageable. I only need to mouse over something and its 'clicked'. I can't get to Add /Remove Progs to remove last installed prog. Can't get to System Restore expt the one time I did get there and str whateve exe or dll did not initialise as system was closing down. Cant get my Avast to scan as its accessed by right click and that menu is flickering off and on and resetting each time. Gone in through SafeMode and the problem is still there. Removed keyboard, changed mice = no difference.
I have no idea other than trying to 'hit' specific areas (sys restore / add remove / virus scan)before lots of other progs are triggered or , as indicated, the system decides to close itself (seems that is getting triggered as soon as i hit Start button). Happily I have a backup pc but its my "good PC " thats Donald Ducked.