It will check your hard drive for possible issues pertaining system files that may or may not have gotten corrupted and are causing your computer to behave erratically, it fixes many errors, and yours certainly sound like a good candidate for this.
Here’s the process:
Restart your machine holding command S
You will get a black screen with text popping in, no interface at all. This is known as the verbose mode. After the screen settles the last line you should read
root#
hit enter and type:
fsck -f
hit enter
the computer will start running a series of checkups on your drive, it will try to repair any wrong files, if any and if possible.
Depending on the issues encountered the process may take 2 minutes or 40 minutes, so be patient.
When it’s done you should read something like:
The volume appears to be ok.
If anything was modified you will read ***FILE SYSTEM WAS MODIFIED***
After that type:
reboot
hit enter.
Your machine will boot normally, now you can try Illustrator again, but before launching hold the shift, alt and command keys, when a message asking to delete the preference files appears click yes.
Hopefully everything should be working fine now.
Good luck and let us know.