I had a similar problem a year ago with my 98 SE as far as the red X. In fact, everything was slowing down and I had DSL. Assume you have IE6. Make sure your cache is cleared by going to Tools, Options, General Tab. Hit Delete Files then check "off line content" then Okay. I had never clicked the "off line" content because I'd never saved anything for off-line use. At least as far as I knew. However, it took the computer 5 minutes to clean out those files. I thought Disk Cleanup would have done it but it hadn't.
You may also have a huge number of other files you don't know about that's messing up your system in ways you can't imagine. If you have Zone Alarm or other firewall program, look for the "logs" section within that application and delete them. I didn't know ZA was keeping daily logs and I cleaned out 4 years worth at one time. Same thing with your anti-virus program. Check other similar programs also - many keep logs.
You can find other buried "logs" by clicking on Start, Find, then type in - with quotation marks "internet logs" and then click on "files and folders." Open up each log file or folder and see what's there - especially if it's large.
I also found out that every year or 2 my ISP changes it's DSL software. Check to make sure you have the most current version. If you have the most currnet version and the CD-ROM is over a couple of years old, get a new one and try it. In 2 instances I found that the then-new CD-ROM had degraded after 2 years and that new CD-ROM of the same software solved a lot of strange problems.
Give this a try and post whether or not it helps. Good luck!
