Hi,
yeah those idiots who make those calls really wind me up and I always give them hell whenever they make the mistake of phoning me..
When you re-installed windows did you change the boot order so that you booted straight from the windows disk? If not, boot into your bios and find the boot order... Change it so that whatever your install media is (disk or USB) is first, eg: CDDVD.
If you have already tried that then either you have a hardware problem or a virus. If you have access to another computer download and burnt to disk an anti virus app.
http://www.sophos.com/en-us/support/knowledgebase/52053.aspx
The above link has information on how to change the boot order and a download for some ant-virus software. (you'll need to...