ENABLE TASKMANAGER

If you have any viruses, then you may notice that they affect to the task manager and disable it
This is because if we know that there is a virus active in our background there’ll be a chance to stop it using task manager.
Disable task manager doing by viruses editing the computer registry.
Here how you can fix and get back the Task manager again.

"Method 1":Click Start >> Run >> and type the code below and press Enter.
REG add HKCU\Software\Microsoft\Windows\CurrentVersion\Pol icies\System /v DisableTaskMgr /t REG

"Method 2":Click Start>> Run>> and type Regedit.exe (open registry editor)
Navigate to the HKEY_CURRENT_USER \ Software \ Microsoft \ Windows \ CurrentVersion \ Policies\ System .In the right-pane, delete the value named DisableTaskMgrClose Registry editor. You may want to restart you computer for changes take effect.

"Method 3":Click Start >> Run >> type gpedit.msc (Open Group policy editor)
Navigate to:User Configuration / Administrative Templates / System / Ctrl+Alt+Delete Options / Remove Task Manager .Double click the Remove Task Manager option.Change the policy to Not Configured and click ok

HOW TO REMOVE Drivegaurd.exe or flashgaurd.exe VIRUS

Drivegaurd.exe or flashgaurd.exe

“this worm will remove all files from C:\heap41a that are related to other malicious programs it enables TaskManager if is disabled” - BitDefender

it also download some other malicious files to your computer

You can locate the virus files at c:\Program Files\FlashGuard\FlashGuard.exe
Or you may have to change the attributes of this folder.For that you can refer this guide
c:\Program Files\FlashGuard\FlashGuard.exe
c:\Program Files\FlashGuard\ReadMe.txt
c:\DocumentsandSettings\**UserProfile\LocalSettings\Temp\DriveGuard.tmp.exe
c:\DocumentsandSettings\**UserProfile\LocalSettings\Temp\gHmpg.tmp.exe
It creates folders in your pendrive & copy itself to :
f:\System\Security\DriveGuard.exe *
f:\autorun.inf *
f: is your pen drive so change it according to your pendrive drive.
Will add itself to startup:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\FlashGuard
To see these virus you must set Windows to show hidden files -
HOW TO REMOVE IT :
Press Ctrl+Alt+Del to open ‘Task Manager’, select FlashGuard.exe & click ‘End Process’
You can browse to the folder mentioned above or you can find it quickly by using ‘Search’ feature(Start Menu>>Search). In the search box type, flashguard.exe or flashguard. Don’t hit the search button ..

Scroll down & expand ‘More Advanced Options’.Check the all the box as you see in the screenshot below & hit ‘Search’ button..
Delete all the files found..
Also serch for .tmp.exe, delete DriveGuard.tmp.exe & gHmpg.tmp.exe files…
The virus files can easily be recognized with pendrive icon and delete those files.
Congrats, the virus is removed from your computer. But still some entries made by the virus files exists in registry.
Go to start->run and type msconfig and hit enter
Select ‘Startup’ tab, select & uncheck FlashGuard. Click ‘Apply’.

Delete Registry Entry : Go to Start Menu>>Run, type regedit & click ‘Ok’
Browse to :
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\FlashGuard
Select FlashGuard, right-click on it & delete