Rear shifting - Unable to shift to toughest gear
The first thing to do with any rear derailleur problem is to check if its bent. If it is bent, go to your LBS and see if it can be unbent (there is a special tool for checking unbent-ness, Park Tool DAG-2 or similar) -- bent derailleurs cannot be adjusted properly in most cases (and even a minor spill can cause a bent derailleur). If its not bent, then try adjusting it. 

If you can't reach the smallest cog with the cable released (assuming a typical non-rapid rise derailleur, i.e. one which goes to the smallest with no cable tension), it likely means your high limit screw is mis-adjusted (too tight). [Typically, the problem upshifting into the smallest cog is usually a bent derailleur/cable friction, but you should have eliminated those two options before you got to this]. 

Some good tutorials for adjusting derailleurs are Sheldon Brown and Park tool.