What is wrong with my hard drive?

I recently had a big computer crash. I’m not sure why it crashed exactly, but the symptoms after were issues with bootmgr and chkdisk and generally with the booting process in general. I installed a clean copy of windows 7 on one of my empty internal drives and its running beautifully. The issue is with the 1 TB SATA HD (also internal) i have on my computer which has almost all of my important data on it.

When I click on the drive in Windows Explorer, it lags really long to display the directory. When I click on a folder, it lags again, which continues to do each time you click on something new. The lag time is somewhere around 30 seconds. What is the problem with this drive now? Would a format fix it? if so, how can i back up my filez????

Any help would be appreciated!