74.41 GB with 3.35 available
This is a serious problem.
OS X needs about 10 gigs of hard drive space for normal OS operations - things like virtual memory, temporary files and so on.
Without this space your Mac will slow down as the OS hunts for space on the disk, files will be fragmented, also slowing things down, apps will crash and the risk of data corruption - that is damage to your files, photos, music - increases exponentially.
Your first priority is to make more space on that HD. Nothing else can be done until you do. Purchase an external HD and move your Photos and Music to it. Both iPhoto and iTunes can run perfectly well with the Library on an external disk.
It's very likely that iPhoto won't open because the Library has been damaged from being run on an overfull disk.
Is there a crash log?
I am using an application called "whatsize"to let me know what is taking the space and whilst I have a lot of pictures and music it is video of an old band I was in that is taking most of the space. I am really struggling to get rid of them as it says they are stored as an imovie project ( some of them are over 5GB !! ) when I look in "whatsize" but when I search for them in "finder" I just cant seem to find them to get rid of them. This would free up about 30GB so would help things considerably.
Any ideas how to delete them ?
Well mking space was never going to fix the problem, just stop it getting worse.
Hog big is your iPhoto Library and how much space do you now have? I ask as the second of these will duplicate your existing library.
Back Up and try rebuild the library: hold down the command and option (or alt) keys while launching iPhoto. Use the resulting dialogue to rebuild. Choose to Repair Database. If that doesn't help, then try again, this time using Rebuild Database.
If that fails:
Download iPhoto Library Manager and use its rebuild function. (In Library Manager it's the FIle -> Rebuild command)
This will create an entirely new library. It will then copy (or try to) your photos and all the associated metadata and versions to this new Library, and arrange it as close as it can to what you had in the damaged Library. It does this based on information it finds in the iPhoto sharing mechanism - but that means that things not shared won't be there, so no slideshows, books or calendars, for instance - but it should get all your events, albums and keywords, faces and places back.
Because this process creates an entirely new library and leaves your old one untouched, it is non-destructive, and if you're not happy with the results you can simply return to your old one.