Hi again
Were you ever able to run any diagnostics at all? If you weren't able to get the Toshiba diagnostics to run, I suppose you could try some generic diagnostics. The Ultimate Boot Cd (the Linux-based version) creates a DOS-floppy-diskette emulator, and can run diagnostics from that - since it would make sense to see if there isn't a hardware problem complicating things
http://www.ultimatebootcd.com/
You could also see if the system will boot & run from any versions of the CD-based distribution called "Knoppix". If it does boot from that (which it will do very slowly, since it runs entirely from the system memory & the CD-drive), then you might be able to get online with the FireFox included in most Knoppix CDs (most do a fairly decent job of detecting the networking chip on modern motherboards - and provide a working driver).
http://www.knoppix.org/ (if the webpage displays in German, click on the US/British flag icon to read it in English - several other languages are available as well).
Were you able to discover if you had the .cab files on the hard drive? Or did you find anyone willing to let you borrow their Win98 CD so you could reinstall? (not a Recovery Disk, though! - a genuine Win98 installation Cd -- and not an OEM version that's bound to a particular company's motherboard [Dell CDs tend to feature locked versions in this manner] . . . )
Since you tried a different OS along the way, it's possible that the MBR is a bit off as far as Windows 98 is concerned. Booting from a Windows 98 installation Cd "start computer with cd-rom support", and running the command "fdisk /mbr" [without the quotes] can sometimes help by restoring a workable Win98 MBR.
See if any of that helps
. . . Gary