Usually, a blue screen is indicative of a conflict in two programs Windows is trying to load and run, or of a program trying to access memory that isn't there. There is a possibility, therefore, that HIMEM.SYS may be corrupt. You can correct that by extracting the file from the .CABS in your setup directory. If your Windows is OEM (came already installed), they are in C:\WINDOWS\OPTIONS\CABS. If you installed Win98 from a CD, they are there in the Win98 directory. (I'm assuming you created the emergency startup disk--I hope you did since this is how you will activate your CD-ROM.)
After you go into the Windows directory where, of course, HIMEM.SYS is, type
extract /?
which will provide the syntax you need to use to extract the file.
If this does not work, then the link to HIMEM.SYS may be missing in the Windows Registry.
You may know this, but I'll tell you anyway: The Registry is composed of two files: system.dat and user.dat. These are found in the Windows directory. In DOS, find what files are there by running:
dir system.* /ah
dir user.* /ah
Besides the .dat files I mentioned, you should see other files with the same prefixes ("system" and "user"

and different suffixes, such as .ns0 or .syd. The system.da0 is the one you are looking for in this case. (I don't believe you should have to mess with the USER.DAT file here.) Check its date. If it are relatively recent but its date indicates it was created before the errant download, you can copy the SYSTEM.DA0 to SYSTEM.DAT.
First, you need to set the attributes of the files so you can work with them. You do this by
attrib -h -r -s system.da?
(The question mark is the wildcard so the command is carried out on both the .dat and .da0 files.) Then you can copy the .dao file over to .dat file:
copy system.da0 system.dat
(NOTE: SOME OF YOUR APPLICATIONS MAY NOT WORK AFTER THIS, AND YOU MAY HAVE TO REINSTALL SOME OF THEM.)
You will get a message wanting you to confirm it, upon which you will indicate "yes." After completing this, restore the files' attributes:
attrib +h +r +s system.da?
Now try to reboot. If it does not this time, you are probably faced with reinstalling Windows. You can do this with either
c:\windows\options\cabs\setup.exe
or
d:\setup.exe
("d" representing whatever drive letter your CD-ROM is sitting on).
Even though Windows will undergo a complete reinstall, all your applications and drivers should still work after this. The only change, essentially, will be that Windows created a new registry.
I know this is pretty involved, but once your Windows will not boot, it becomes close to your only recourse.
Butch
"It's what you learn after you know it all that counts"