problem starting - wont turn over at all

Hi! I'm new here. I have a 1996 GMC 3/4 ton 4x4 pickup with 253000 miles and a rebuilt motor. It usually runs great. Yesterday i went to start it and it turned over once and didn't start and then died. The radio and hazards and stuff work, but there is nothing when i turn over the key. Sounded simple - i pulled the battery and starter and celenoid (sp?) and took them to the store to get checked out. They all check out fine. I really cleaned all the cables and it still won't start! Seems like there is a fuse or something but i can't figure it out! I sure could use some guidance!!! Thanks!!! don