Hi Nigel, you've probably used up all your back-up space, which is why you can't restore to an earlier time (at the mo.
Steps I'd follow in this situation:
Go to
http://housecall.trendmicro.com This is a free on-line virus cleaner that is always up to date
Go To
http://doxdesk.com There are Free Spy/hyjack removal tools available via that site. (personally, I use services of
www.tomcoyote.org/hjt with Excellent results
To get back the use of system restore - you'll need to switch it off - which will clear out all previous 'saves & restore points' to make room for new one's. Before you do this though, you need to fix any other issues or instabilites that maybe corrupt I recommend you back up important documents to disk (incase the worst happens- it hasn't for me... yet
The computer will warn you against turning off system restore regardness of how stable your system is
Once system restore is turned off you need to restart you computer - then you straight back to the system restore wizard & turn it back on - then you can decide how much space you want to use for the restore feautre in the future. (I always use the maxium amount & give it a clear out every 6 months or so:
you can then create a new restore point.