Hi there Nekoplexis,
That is really unpleasant.
You should have backed up the data stored on the drive the moment that these weird things started. Mechanical drives could sometimes just fail. You should always back up the data you can't afford to loose.
Is the chkdsk process still running? Is the drive recognized under My Computer and Disk Management?
If the drive is not recognized or inaccessible for some reason, you try some of these tools: https://www.lifewire.com/free-data-recovery-software-tools-2622893
You need to recover the files to another drive.
Once you've done that, you can see what is wrong with it: http://www.tomshardware.co.uk/forum/282651-32-best-diagnostic-testing-utility
If you have a spare USB cable, it would really not hurt to attach the drive with it to another USB port.
Keep in mind that if the data stored on it is extremely important, your safest bet would be to contact a data recovery company.
Let me know how this goes,