Method 1:
Go to registry editor by running regedit in the run box.
Go to this key:
HKEY_CURRENT_USERSoftwareMicrosoft
WindowsCurrentVersionExplorerAdvanced
In the right hand area, double click hidden and change the value to 1.
Now you’re all set to go. Check it in your tools menu if the changes have taken effect.
Method 2: (By Random Hajile)
1. Click “Start” -> “Run…” (or press Windows key + R)
2. Type “regedit” and click “Ok”.
3. Find the key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\ExplorerAdvanced\Folder\HiddenSHOWALL
4. Look at the “CheckedValue” key… This should be a DWORD key. If it isn’t, delete the key.
5. Create a new key called “CheckedValue” as a DWORD (hexadecimal) with a value of 1.
6. The “Show hidden files & folders” check box should now work normally. Enjoy! 
Method 3: (By Denny)
1- Click Start –> Run –> regsvr32 /i browseui.dll –> enter
A confirmation message will appear like given below
2- Click Start –> Run –> regsvr32 /i shell32.dll
Wait for the confirmation and click OK.
