Is he running XP? Tell him to try and boot into "Safe Mode with Networking" (reboot while tapping F8 repeatedly). He should be able to access the Internet through Safe Mode with less programs/spyware/viruses running on his system.
Whether that works or not, tell him to download
HijackThis (or you can download it for him). Unzip the file, run the program (
but do not fix anything), and save the log file. Copy and paste that log file (along with a description of your problem) into a new thread in the
HijackThis Log Help Forum. The analysts there will comb through the log file to check for any infections and they will provide you steps to help clean your system, and hopefully get it running properly again.