My back up drive was disconnected from the Time Machine. Now when I plug it in it doesn't show up and neither do my files. Please help.

Have you done a PRAM reset, CMD+Option+p+r...

http://support.apple.com/kb/HT1379

In fact, do 3 in a row, takes a bit of time.

Intel-based Macs: Resetting the System Management Controller (SMC)...

http://support.apple.com/kb/HT3964

Did you maybe enable iCloud Drive?

Start with this if IntelMac...

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode? Could take 10 minutes.

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.

The pages showing all of my files in Word and Excel suddenly went blank. How do I restore them?

[Email Edited by Moderator]