Shimano Deore Rear Derailer Problem

I'm attempting to figure out why my right shifter - rear derailer will only shift on the four outer most cogs. I cannot shift to the four inner most cogs.
I bought a used Marin mountain bike this fall. It's equipped with Shimano Deore front and rear derailleurs. The rear derailleur (8 speed) only shifts between the highest four cogs. It works accurately and smoothly. However, the shift lever does not seem to connect the get to the lowest or inner most four cogs. I assume that it simply needs to be readjusted. It seems like this is something that would require a change to the limit stop screws. I'll try to dig into this over the weekend.
These are some web sites that I have found good reading so far.
This site had some good content.http://www.parktool.com/repair
This is a very good site to learn about Derailers.http://sheldonbrown.com/derailer-adjustment.html
Shimano Techdocs - This might be helpful.http://techdocs.shimano.com/techdocs/index.jsp

Cleaning Off Finish on Frets

Here is the neck from a Double Fat Strat I have been playing. This one I have re-assembled recently. I bought a Fender licensed Allparts 70's Strat neck a while back and I used this neck on the project you see here. As I started playing I noticed there is a large amount of finish on the frets. The finish was chipping off as I play (see circled places on the frets). Of course, this creates a real uncomfortable feel on bends. It's like hitting a speed bump. Also, I doubt you get the best sound possible with finish on the frets.





I taped up the frets with masking tape. Then I got a razor blade. Then I taped off the ends of the razor so as not to gouge anything else. This left a spot in the middle of the razor that is bare. I scraped off the finish from each fret. Don't worry, you won't wreck your frets. Just make sure you pull it across the fret, not push it. When I was finished I was careful when removing the tape. I removed it slowly, so as not to pull any of the finish off between the frets.

What an improvement. The finish on these frets was on thick.You can see from the photos that the chips of lacquer made a mess. It was worth the effort.