Sounds like a Trojan or virus.
Windows itself would NOT remove an important item
like "systray" " explorer",so something else is doing it.
Best bet is virus or worm.
Try this.
Go to...
C:\windows\options\cabs\setup.
Use the setup that has a computer as an icon.That`ll
reinstall windows without you loosing all your data.
Make sure though to Move whatever you have in "My
Documents" and "My Briefcase" to some other spot on your
puter.Maybe in "new folder" on your C: drive,better yet
if you don`t have a lot there,put the data on Floppys.
But FIRST,I`d check for a virus.
If the entry has disappeared from MSCONFIG and is
available they can be copied back into the appropriate OS
StartUp directory:
Win9x/98/Me - C:\Windows\Start Menu\Programs\StartUp
Also try this.
Start,run.
Type in Msconfig>Look to see that it says "normal startup"
If not,check it.See if that brings back the missing
entries,although I don`t think it will.
Go to these keys to see if your progs are still listed.
HKLM\Software\Microsoft\Windows\CurrentVersion\Run
HKLM\Software\Microsoft\Windows\CurrentVersion\RunOnce
HKLM\Software\Microsoft\Windows\CurrentVersion\RunServices
HKLM\Software\Microsoft\Windows\CurrentVersion\RunServicesO
nce
HKCU\Software\Microsoft\Windows\CurrentVersion\Run
HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnce
>.
>