There may be other reasons for freezing, crashing, missing functions, tools, or other things such as a key seemingly being permanently activated, that might otherwise seem to suggest corrupted preference settings.
When it is not something in the Adobe Illustrator CS4/CS3/CS2/CS Settings folder (Adobe Illustrator 10/9/8 (without Settings) folder for pre CS versions), you may try each of these options with tests, closing and reopening Illustrator for each test:
1. Corrupt font(s): you may move all (non system) fonts out of the Windows fonts folder (or the corresponding Mac folder) and move them back in; font moving may be done in groups; this is reversible.
2. Firewall interference (especially if more than one is running (some OS add one if activated)): you may turn them off (disconnected from the internet) and on again.
3. Some versions of Acrobat generate many temp files. Too many (64K) causes the problem: you may search and destroy Temp files.
4. Some other inconsistency caused by Adobe Acrobat/Reader: you may try uninstalling and reinstalling (a newer version). A solution to the special issue of (InDesign and) Illustrator CS/CS2 failing to launch after installation of the Mac OS X Acrobat 8.2 update is presented in this Adobe TechNote.
5. Incompatible/old printer definition file for the default printer: you may upgrade the driver, change the default, or set the PostScript driver/PDF to default.
6. Using a US/English version of Illustrator with the OS set to a different language, or the reverse: you may enter Control Panel>Regional and Language Settings and change to English (or similar for Mac) and change back.
7. Interference from other applications, seemingly a great number of possibilities including (the list will be updated):
Close down all possible suspects, and try opening them one by one; if necessary uninstall, and in some cases (including Quicktime) make sure the programme folder is deleted.
8. Interference from other Adobe applications running at the same time as Illustrator: Close down all Adobe applications, and try opening them one by one; if necessary delete the preferences of the offending application(s).
9. Interference from other applications running at the same time as Illustrator when a key seems to be permanently activated and the application can be activated by it as a hot key: Close down all relevant (or all other) applications, and try opening them one by one.
10. An application programming interface (API) bug in MAC OS 10.6.5 or 10.6.6:
Restart you computer, and then run this utility:
http://www.bache.name/download/osx/10_6_5 keyboard hack.dmg;
you may see the explanation to go with the suggestion in this Adobe Forum thread/post:
11. A font caches issue: Clear the font cache; instructions may be read here: http://www.fontmarketplace.com/info/font-help.aspx; there are font caches clearing applications for Mac, searchable with the search term clear font caches.
12. Missing palettes: Copy the relevant plug-in from the C:\Program Files\Adobe\Illustrator 10\Support Files\Required folder to the C:\Program Files\Adobe\Illustrator 10\Plug-ins\Extensions folder, or between the corresponding Mac folders.
13. Other settings a): Delete or move other files/folders in the same folder as the Adobe Illustrator CS4/CS3/CS2/CS Settings folder (Adobe Illustrator 10/9/8 (without Settings) folder for pre CS versions), see Move the Folder to locate it; this is reversible.
14. Other settings b): Delete or move other files/folders elsewhere depending on the issue; this is reversible.
15. Undo recent changes: If none of these possible solutions work, consider whether you have made any (other) changes to the (Win or Mac) PC between succes and failure, including new software loaded; you may undo the changes.
After each attempt Restart Illustrator, and see whether the issue is solved.