when she is offline internet explorer pops up with different advertisments. Why? And window after window keeps popping up also. the windows also starts flashing. I really don't know how to explain to well when it comes to her computer, but any answer is helpful. thank you.

http://forums.spywareinfo.com/index.php?showtopic=60955

The system is infected with malware. Make sure you run up to date anti-virus and adware detection software (such as AdAware from http://lavasoft.com/ ) on it.

You should also consider replacing the operating system on the machine. Windows 98 has past end of life and security fixes are not longer being produced for it.

There is a virus installed in that computer try to install any antivirus and scan full harddisk for virus.

Her machine is badly infected with malware. She must do a complete system scan with both her anti-spyware and anti-virus programs.

Windows 98 has not been supported with Microsoft critical and security updates for years, therefore it is a "magnet" for all sorts of malware (viruses, worms etc). Plenty of vulnerabilities for the black-hats to exploit.

Honestly, your friend needs a new computer with a modern operating system (Vista or XP) more than anything.