A hard drive failure would be coded 4HDD; All 4MOT errors are cooling fan errors. Your error message is reporting a problem or outright failure of the hard drive's cooling fan. Not quite the expense but, as rkaufman says, BACK UP NOW! The lack of a cooling fan (4MOT) coudl cause the hard drive to fail.
The fan is buried at the bottom of the comuter case and replacing it is not an "at-home" task for even a reasonably adept home user. This picture from the iFixit web site shows the HDD cooling fan's position after almost everything else has been stripped from the computer:
Unless you are quite the computer disassembly expert, you'll need professional help to fix this one.
Slowdowns are more commonly due to software issues. Anti-virus apps, so-call "cleaning/optimizing/tune-up" programs, and some online banking security software slow more browsers that bad hard drives. So can incompatible browser plug-ins.
You can safely give us a snapshot of your config so we can see if you have any well-known bad software actors that can contribute to slowness. Please download and install this free utility:
http://www.etresoft.com/etrecheck
It is secure and written by one of our most valued members to allow users to show details of their computer's configuration in Apple Support Communities without revealing any sensitive personal data.
Run the program and click the "Copy report to clipboard" button when it displays the results. Then return here and paste the report into a response to your initial post. It can often show if any harmful files/programs are dragging down your performance.