Fonts folder has lost its system properties.
This will be obvious if viewing the fonts folder. You will not have
the names and the "Install new font" option under file.
If so:
Check the protection in Properties on folder c:\windows\fonts
If it is not shown with a check in System, then you cannot install
new fonts. It should also be protected, so you may not be able to
alter from Explorer.
In DOS mode, (or from Start-Run) use the command
   attrib +s c:\windows\fonts
Reboot and all should be OK

or...
Use TweakUI
Tweak UI 1.33 for Windows 2000, Windows NT, Windows Millennium
Edition, Windows 98 or Windows 95.
Details at: (may wrap)
http://www.microsoft.com/ntworkstation/downloads/PowerToys/Networking/NTTweakUI.asp
Download at:
http://www.microsoft.com/windowsme/guide/tweakui.exe

The system attribute is is normally the problem and the DOS fix is the
solution in the majority of the last few hundred responses I have made
to similar problems. The Fonts folder will not function as a special
folder without the system attribute. The other common problem is that
the hidden desktop.ini is missing or corrupt and TweakUI will fix
that.
There is a third problem mentioned here but, in my experience, this
one is uncommon.
(Fontext.dll file may be missing or damaged)

Missing Menu Commands in the Fonts Folder
http://support.microsoft.com/support/kb/articles/q133/7/25.asp

...Alan