Pete - thanks for your help. Malware bytes didnt pick up anything. However, from checking microsoft answers it seemed a lot of people on vista were having problems with the upgrade to internet explorer 9. The problems on my laptop started around the time of the upgrade so i have deleted ie 9 and reinstalled ie8 using instructions on microsoft site. I also went into control panel, personalisation, appearance settings and changed the resolution and changed the display to windows classic. This seems to have put things back as they were but ive no ideas how they changed in the first place!
Everything looks ok now, fingers crossed!
Thanks very much for your help.