Windows 98 Start-up Error: Explorer performed an illegal operation. Invalid page fault in module EXPLORER.EXE.

Model:  Dimension XPS T700r.  OS:  Windows 98se.  System had been working well since May 2000 until it died a couple of days ago.  (i'm typing this on my laptop). 

The error at the end of the reboot is as follows:  EXPLORER has performed an illegal operation and will be shut down.  If problem persists, contact the program vendor.  Details:  . . invalid page fault in module EXPLORER.EXE at  019f.00401f31 . . .

I don't even know where to begin to fix this problem.  Any help will surely be appreciated.