That's the key. It sounds like a virus to me, it's trying to prevent you from killing it. Because you can't reliably run a virus scan, your best (and cheapest) bet is to reinstall Windows. Have a computer tech pull any documents you need from your HD. Take the HD out yourself and bring it to them to save extra $$.

Install from the Windows disc included with your machine. DO NOT use the drivers on the CDs! Instead, after you've finished installing Windows, go to support.dell.com and get the most recent drivers.

Dear XISOP:

Thank you for the advice. I figured this was the only way to resolve the issue, and that it was, indeed, a virus.