Please tell: What fixes did You try - that didn't work - so we can omit them.
A. Corrupted iMovie pref file - very common problem
- Trash all iMovie pref files (or rather to test this - start a new User Account / Log into this - if iMovie now works OK then the problem most likely is here)
B. Correpted iMovie movie project - the other project's run's well
C. iPhoto - Corrupted iPhoto Library
- THIS TAKES SEVERAL HOUR TO MEND and
- YOU need lot's of free space on Your Start-Up (Macintosh HD) Hard Disk - else it might crash !
To me it takes about 24 hours - AND I CAN NOT use the Mac during this time (just to prevent it from HANGING and destroying more than can be fixed)
Start iPhoto - BUT KEEP option-key AND cmd-key down during all up-start.
Now You got a list to select from - SELECT ALL
IF a Lap-top - CONNECT Power-Mains - Battery will not last !
Do something else for lot's of hours.
When its done - Close iPhoto
Open iMovie and see if it now works OK
Good Luck !
Yours Bengt W