Well I think it's fixed now...I found the answer here:SIDEBAR.EXE MISSING
This is what I did, I have no clue why it worked though...
Jeremy M is right...it ought to be reachable from there. If it isn't, you might need to re-register some necessary dll files.
1. Click Start
2. Type "CMD" without the quotes
3. Right click cmd.exe and select 'Run as Administrator'
4. In the command prompt the pops up, type the following:
Regsvr32 -u "%ProgramFiles%\Windows Sidebar\sbdrop.dll"
Regsvr32 -u "%ProgramFiles%\Windows Sidebar\wlsrvc.dll"
Regsvr32 "%ProgramFiles%\Windows Sidebar\sbdrop.dll"
Regsvr32 "%ProgramFiles%\Windows Sidebar\wlsrvc.dll"
5. Reboot the computer.
See if this brings back your sidebar.
I hope this helps!