My only suggestion is if your friend has backups, full (long) format the drive, then clean install everything starting with Windows. And see how that works.
Otherwise, and especially if your friend has no backups or it still works poorly after the above, just buy a new drive and use that. Then, getting the computer up and running again with a clean Windows install, attempt to recover stuff from that drive.
chkdsk can only attempt to correct things. It just can't fix everything :)
You can see what someone else suggests. Personally, I wouldn't try anything else here as it will all be likely to have issues, end in failure, or total file loss (besides attempting recovery or paying for recovery specialist) if its not all lost already.
If you want to minimize time and risk then simply skip to the second one and buy a new drive. Its the way it is. After, can always use the current drive as a secondary drive or even an extra backup drive if its data isn't necessary and full format works and its more reliable after.