Totally frozen!!!!

I need major help with my computer! I am using Windows 98 and my computer has been freezing up. It will freeze completely, the screen will freeze, the mouse too, and I can't use ctrl+alt+del. The only thing I can do is give it a hard shut down and then power it back on and relog in. It doesn't have a specific pattern, it will freeze at any time, when I am online or offline, and timing doesn't matter either. Sometimes it'll freeze right away, or after i've been on for awhile. I've tried to run Spybot and it doesn't seem to detect the problem. I also have ZoneAlarm as my firewall, and run Avast! anti-virus too. My IP provider is AOL dial up(free trial version). I am sort of computer literate, I have been learning everything "hands-on" from just being on the computer and having to fix problems myself, so please give any info that could help me. I would REALLY appreciate any help at this point. I am so frustrated by this problem, especially when I am in the middle of something important and have to reboot!!