who are these 'rental' machines from ??? -

I look after 18 in the UK and tend to rebuild from scratch if they've been out for a long time. Some shorter gigs only get 'cleaned' but thoroughly tested, and re-build if not up to spec and I;m not happy with them.....

1st advice is - Check all the settings and ensure that it is in optimal performance and that theres nothing else running in the BG. Also check the ATI panel settings and disk permissions....