Sounds like you have a corrupt font(s) loaded. If you use a font manager disable all but the system fonts and see if that helps. Illustrator is far more sensitive to font corruption than Photoshop so do not assume.

If not create a new user account log in to that user account and launch Illusttrator and see if that has any effect?

You can try this as well.

PC

1. Quit Illustrator.
2. Rename the AIPrefs file (for example, to AIPrefs.old) in the Users/(user)/AppData/Roaming/Adobe/Adobe Illustrator CS5 Settings folder.
3. Start Illustrator. Illustrator creates a new preferences file.

Mac

1. Quit Illustrator.
2.Go to User/username/Library/Preferences/ Adobe illustrator CS5 Settings and trash the settings folder, the whole folder not just the contents of the folder.. You can also simply rename the folder to old settings.
3. Start Illustrator. Illustrator creates a new preferences file.

I am having the same problem! Would love to hear thoughts on a working solution....

Thanks

Oops sorry, didn't see you're reply.

Ok, so I am now leaning towards a corrupt font also like Wade Z. suggested. A few things to try if you haven't first though.

1.) Did you repair permissions using Disk Utility in the Applications > Utilities folder? I'd do that and run it a few times until it runs "clean". Meaning that you don't see it repair anything anymore in the list. (I'm assuming you're on a Mac). If you're on a PC this won't help.

2.) You could try resetting the PRAM etc., but I don't think that will help this problem. Sometimes you never know though.

So, if it is a corrupt font, I need to know if you are using a font management program or if you manually place them in font folders? (again assuming you're using a Mac). Post Script Type 1 fonts are known to be more finicky to use in Snow Leopard and Lion. I had some problems with duplicate fonts that were causing havoc on my machine just a few weeks ago. So you may want to try and track down if you have duplicate fonts also. I just used Spotlight to find where any errant fonts were installed. If you install fonts manually I'd temporarily remove them all from the User > Library > fonts folder (or wherever else you may have installed them) and then restart. That way you can test to see if that might be the problem. Then if it is you can add half the fonts back in and do a bubble sort to find which font is corrupt. A bubble sort is a way of taking half of something and testing if it's good or bad. Then if it's a bad half, taking half again to see if it's good or bad. That way you can narrow in on a specific file causing the problem. It can be a little tedious with having to restart, but is one of the best ways of finding a corrupt font. Another method may be to remove all of one type of font and add each set in until  the problem shows up again (if removing them is what fixes it).

If you use the built in FontBook you can try this: http://www.lifespy.com/2007/mac-tips-find-and-eliminate-corrupt-fonts- in-osx/

Hopefully you'll get it worked out.

It is very good that you found a resolution for your issue and tthat you marked the response as answered, it will I am certain help other users who encounter this problem.

Hi,

This is late reply but I had this same problem today and maybe i could help someone else.

I tried absolutly everything people suggested on this and other forums but nothing worked.

What I did in the end was go to Library>Fonts and scrolled down.

I noticed some font files didnt have thumbnail like the rest of them, they just had the Font Book Logo instead of a sample of the font. I selected all these files and moved them to a new folder on the desktop.

I reopened Illustrator and everything was fine, I could open the font menu again without it quitting on me.

I'm not sure what those files where or how they got there but deleting them certainly worked. I have kept them on a old pen drive just in case I find out I do need them one day.

Hope this helps