Is this Vista SP2? Also do you have any other security software installed? Also any strange popups indicating infection?
Try running the McAfee Virtual Technician to see if it will repair the installation.
If that doesn't help, try the following...
Uninstall all McAfee via Control Panel/Programs/Uninstall a Program
Download and run the MCPR removal tool and reboot immediately.
Go to your online account page and download/install your products again.
If you've been using Registry Cleaners and Optimizers or System Restore, this can sometimes happen.
Is my laptop exposing to danger in this situation?(unable to run scan)
That's Windows 7.
I didnt installed any other security software and there are no strange popups.
If i uninstall the program, and download back the program would it affect my product registry?
I just purchase McAfee 2 weeks ago and it frusted me already. I have no idea how i can survive with McAfee for the following 14 months=(
No it's OK and Windows Firewall will enable itself during reinstallation so you are protected. If you need online help from McAfee staff it is available through Technical Support Chat - see Useful Links above.