It is possible your McAfee installation has become corrupted. I recommend running the Latest Stinger (Read How to use),Getsusp,and followed up by Malwarebytes (Free) Version for another opinion.
Note; When running McAfee Getsusp, please remember to enter your Email address before Scanning.
These Superb (Free) tools can be found in the inserted Link below:
In addition you can run the Latest McAfee Virtual Technician to scan for issues with your McAfee Product:
Should there be issues found by MVT, in which it could not resolve, you can follow the Guidelines/Instructions in this Link:
Note: I neglected to ask, does your McAfee scan (Stop) or Seemingly (Hang)? For there is a known issue in the past, that has a "Workaround"
Edited; to add more content
McAfee Volunteer Moderator
The hang is at Finding rootkits ( when they really mean looking for )
If not here follow CD's advice It may be necessary to uninstall reinstall your Mcafee product as per CDs last link
Please let us know if the previous suggestions resolved your issue with the Scanning Issue