full disk

I have 5 yr old macbook with intel processor. My hard drive is full and I've been using an external hard drive to keep the machine going but now I get a full disk prompt that recommends I delete files but I can't even log in to my user to do this. I'm not sure if the computer locks when all the hard drive space is used and I cannot go in and delete any files now. The computer start just fine and I'm able to select my user and I put my pasword. The computer starts to log in and basically my wallpaper shows but thats it. No icons show up and I basically can't do anything. I'm able to shut the computer off normaly but that's it.

Any advise would be appraciated.

I'm trying to hold on to this laptop with the idea of buying a new Imac when they come out but I feel like I may just have to buy a new computer now rather than later.

Thanks in advanced for the advise