Ok, that info is a little patchy - the exact Pavillion model number would help.
Is it Windows 98 or 98SE? Right click on 'My Computer' select 'Properties' and the 'System Properties'(?) window should open. On the first page it tells you your Windows version.
Don't worry about cleanmgr, instead navigate to the Control Panel then double-click Internet Options.
This opens the 'Internet Properties' window.
In the 'Temporary Internet Files' section click the buttons 'Delete Cookies...' and 'Delete files...', tick the 'Delete all Offline Content' box when prompted.
Then click the 'Settings...' button and set the reserved disk space to about 200MB (if it's already lower leave it there) - you shouldn't need more than that.
Click OK to exit out again.
This just cleans out unnecessary files to make the scans faster. Now do the scandisk and defrag in Safe Mode as in my earlier post.
Oh, yes. Hard drive free space in Win98 - double click 'My Computer' right click on the 'C:' drive and select 'Properties' this should open a window with a pie chart diagram of the hard drive space. It should say below it xxxx bytes free or xx% free. Post the info back here please.