Startup disc too full to start up!

I have a 4 year old IMAC that has been used as our family "mother ship" for I Photo, I Tunes...etc. As it got more use, the hard disc continued to fill up which I supplemented with external hard drives moving the I Photo library over and other files to keep the IMAC running smoothly. I would get the warning that the start up disc was nearly full numerous times and would move over files. Unfortunately, I do not use this computer regularly and the boys kept using it adding music etc and not letting me know about the start up disc warning. Now, it has finally given out on us and won't start up. It boots, and asks for my login password, but then it just goes to the start up background, but the program icons or anything else ever shows up on the screen. I think it really wants to start up if I could just create some space for the start up disc, but I can't get to it. Any thoughts? I tried starting up in safe mode to no avail.

Thanks

Do you have another Mac? If you do, you can start the iMac in Target Disk Mode and then delete or move files off the drive.

Otherwise, you may have to remove the old hard drive from the iMac, install a new one, (large) format it and install OS X. The old hard drive can then be put in a USB carrier and the data can be accessed and moved back to the new drive.