Hi Ian
There could be a number of reasons but this is what I'd do
1. Under Tools - Options - General
have a look at what homepage it's set at. It could just be that particular site causing the problem. Has it changed from what it used to be? If so, change it back to a blank page or to something like
http://www.google.com/ or whatever you used to have. Click 'Apply', exit and re-start IE8. If the next time you start the browser a dodgy homepage URL is showing again, there could be a problem that some sort of spyware has 'hijacked ' the browser.
2. If it hasn't changed and you're still having problems I'd then clear out the cache and cookies (from the same menu Tools - Options - General )
3. If that doesn't work maybe it's an Add On causing the problem so you could try Tools - Options - Programs - Manage add-ons and disabling and enabling them to see if that helps.
I'm a Firefox user too and rarely use IE but every now and then a badly designed website or script will only work with IE so it's good to have to fall back on.
Hope this helps
Best wishes
Rosemary