Help! System problems

Thanks for any advice in advance. My system is an Abit KT7 Raid, 900 mhz Athlon, Geforce 3 ti 200, Audigy card, Lite-on cdrw, Lite-on DVD, 256 PC133 generic, network card, Maxtor 5.2, IBM 20 gig, Seagate 40 gig. Running Win 98.

I've had the system for about 2 years based on mobo age, with certain components newer. However, most of the system has not changed in the last year and a half. Only recent hardware is change of mouse to ms intellimouse over Christmas break. Here is the problem. The system has generally run fine for the last few years. However, in the last 2 weeks it has been freezing a lot. I thought it might have been somehing like a virus or drivers or something so I was going to wipe m C drive and reinstall for a fresh start. Unfortunately, the system has been getting worse to the point I don't even know if it will start up to even do a rebuild. Now the system often won't even post or will just start to boot, but barely get beyond the memoy test. It even freezes when I am in the bios setting screen. This doesn't seem like a windows problem. I cleaned out the case (lots of dust build up) reseated most of the cables, cards and ram as well as reapplied a fresh layer of artic silver on the cpu. I thought it might be the cpu overheating as it did have a problem with this for about a week about a year ago. Right now it runs around 39 c to 42 c under normal load. Which I think is a little hot for this processor. I also thought about getting a new battery for the mobo, but I haven't done that yet. One of my hard drives occasionally makes odd noise, but that doesn't seem like a reason not to post or freze in bios. Anyone have any ideas or help. Like I say, the system has mostly run fine for the last 2 years. Thanks for the help.