Hello!
How is your resident protection set up? I.e. when you click on the resident protection settings in the system tray and select Standard Shield, what sensitivity have you set? If you select "Details" to show the advanced configuration window and press the Customize button to set the options for Standard Shield, what are the settings on the 4 pages you'll see?
What OS exactly do you have? Win98 or Win98SE?
I guess it's useless to ask when you say you get green lines across the top of the screen (it looks like the system is completely dead), but anyway - if you wait for a while (e.g. 3 minutes), does anything happen (like, the avast blue icon starts to rotate again for a while)?
Do you have any special low-level software installed (something concerning the CD-ROM or IDE controller, burning software, CD emulator, ... any other antivirus or anything similar to the resident protection, some kind of disk monitor...)?