Back up your personal files Immediately, and daily until it is replaced.
Clone and replace the drive ASAP (today, tomorrow, as soon as possible).
If you cannot replace immediately and have an external drive with enough capacity, make an image of the drive (Windows Back Up) and make a Windows 7 Repair Disk (from the Back Up section) to be able to restore the image to the new drive if the old one dies before you can get the new one installed.
During the cloning or image restore process, some errors from the original drive may be carried over to the new drive, but if you do it soon enough, these may minor and be able to be ignored or repaired, if you wait for it to get worse, only a reinstall of the OS and programs and a restoring of your back up will get you going again.
You have to be a little bit crazy to keep you from going insane.