iPhoto not "skimming" when moving pointer over events or faces

[afd]

Recently, after my '11 iMac has stopped skimming photos in events and faces.
I've tried rebuilding the library, but it stops at 65% and I've also tried re-installing iPhoto. Nothing has worked.
I even tried using another unused account but that didn't work either, which maybe means it is iPhoto at fault not my iPhoto Library?
Or have I somehow turned skimming off in some obscure setting somewhere?
I'm running Lion and using a magic trackpad, but shave tried a mouse too.
Any help would be apreciated.

 

[afd]

just tried iMovie, skimming doesn't work there either.

edit
Fixed now, was either due to my Logitec wireless mouse that caused problems with my last iMac, but seemed fine with this one, or it was deleting and reconnecting my magic trackpad. Noticed that mouseovers and contextual menus wouldn't work either so thought it was mouse or trackpad.