Rename the folder with games and create a new game directory in Steam. Then copy your games from the renamed folder into the new directory you set up in Steam. Then initiate the download and it should detect the data already there and skip the download. You can also try repairing Steam by downloading the installer and running it with the "Repair" option. Do not uninstall Steam and reinstall it as that will delete your games. --- MacBook Pro with Retina Display | 15.4" 2880x1800 | Core i7-3615QM @ 2.3GHz | 8GB DDR3 1600MHz | GT 650M 1GB GDDR5 | 256GB SSD | OSX 10.8.5 | Windows 8 Pro
I wouldn't mind doing that for each game if I didn't have ~200 games downloaded. --- i7 3770k @ 4.5GHz  HIS IceQ X^2 7970 |1200|1600|3GB|  16GB Ripjaws Z 1866  ASRock Z77 Extreme4  250GB Samsung 840  2TB Barracuda  CX 600 PSU  H80i
<steam or alternate folder>/steamapps/common/<insert game folder here>
It has to be in that location for steam to recognize it regardless of the alternate location.
As mentioned already try to start a download in the location you want then pause the download and copy the files manually. Instead of trying to use the current location you have make a new one on the same drive and then copy the contents of the already downloaded files over.
Again make sure its in the proper folder. --- 2500k @ 4.4 | P8Z68-V Pro | H80 | 8GB | 670 | 256 ssd | 6Tb hdd | Win 8 64bit | ax1200w | BD burner | cm690II Steam: DV8ing1
I never remember it being this big of an issue when I previously had to reload my OS. --- i7 3770k @ 4.5GHz  HIS IceQ X^2 7970 |1200|1600|3GB|  16GB Ripjaws Z 1866  ASRock Z77 Extreme4  250GB Samsung 840  2TB Barracuda  CX 600 PSU  H80i