Transmission will not shift out of first gear?

When either in drive or when manually shifting, the car will not shift out of first gear. Transmission fluid is still in good shape, and it is full. There are no leaks that I have been able to find either. Could this be a shift solenoid issue and are the solenoids internal or external? Or maybe a plugged filter? I ruled out the possibility that the linkage may be out of wack seeing as even if I manually try to shift the gears it still just stays in first. I could be wrong on that though. Any advice or suggestions as to where else to look for a problem would be greatly appreciated as would some diagrams/troubleshooting steps for my transmission. Sorry but I cannot afford a service manual right at this moment. Looking forward to hearing back and thank you for your time on this.