I have a program on my computer from Trend Micro, called PC-cillin. Have had no problems getting "infections" since I installed it. You can even run a spyware/adware scan on your PC from their site for free, to see what is gumming up the works for you.
I still think, though that you should have your friend over to fix your computer. It's amazing what an expert can find and fix on an adware/spyware/trojan infected system.
Back up what you can from your computer onto CDs, you know, documents, special e-mails. In order to realy fix the problem, your friend might have to 'wipe' the system and re-install everything.
agnes!