task manager folder is missing

Taskmgr.exe is a Windows system program, not a folder. Have you checked in C:\windows\system32\ to see if taskmgr.exe was there?

A virus/trojan/malware may have renamed it, I would run a scan with your Anti-Virus and Anti-Malware programs to see if you are infected.

Your windows 7 is 64 bit OS. You will have a taskmgr.exe (64-bit version) file in C:\windows\system32 folder and also another copy in C:\windows\winsxs folder.

There will be a 32 bit version of taskmgr.exe in C:\windows\sysWOW64 folder and also a similar copy in C:\windows\winsxs folder.

If you do not find the taskmgr.exe file in C:\windows\system32 folder, search for the file in winsxs folder. You may pickup the 64-bit version file copy from C:\windows\winsxs folder and copy back to system32 folder. You may have to login as administrator to do this.

Don't go copying things from winsxs. Use SFC instead.
SFC /SCANNOW Command - System File Checker

run sfc as logicearth suggested, sometimes you have to run it 3 times.

Did you try scanning with Malwarebytes Anti-malware scanner and a good antivirus program as suggested by strollin?
If SFC /scannow has not worked for you, you may try the following tips.

A. Try to go to a restore point when the taskmanager was working.

or

B. Follow this procedure
1. Download sysinternals suite from microsoft technet and unpack.
2. Find and run procexp.exe.
3. Click in Options menu on Replace Task Manager and than Restore Task Manager.
4. Click Ctrl+Alt+Del or on taskbar Run Taskmanager.

or

C.Click Start, then type regedit.exe into the Search box and click OK.
Now navigate to this key: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
On the right you will see the value "DisableTaskMgr".
Double-click it, then replace the "1" with a "0".

If you do not have this key in the above location then simply close regedit program.

After these procedures check to see the taskmanager is working or not.