Bicycle Mechanics - Smallest sprocket no more

I was trying to adjust the rear derailleur to get smooth shifting and then I adjusted the barrel adjuster on the rear derailleur, I got it up the the second smallest sprocket and then, I could never shift down again. I have tried everything, adjusting the screw, in fact taking it out but I still can't get it. I loosen the cable with the barrel adjuster at the downtube and I still can't get it. What should I do??

loosen the limiting screw.

Look into the workings of the rear mech and you will see 2 small limiting screws. One of them will be butting up against a part of the deralleur when you have shifted the mech to the limit. Back off that small screw a turn or 2 and you will be able to move the mech a bit more. If you back it off too much, the chain will pop off the small cog and may jam between the cog and the frame.
Dont turn the limiter screw for the large cog, or the chain may fall off and jam between the cog and spokes.

I say bent hanger.......

Well, I got it fixed. I figured out that the barrel adjuster was all the way out of the rear derailleur and I was trying just too hard to screw it in. Then I found out that it was unable to screw in because it is just not straight in. Thus, I changed the direction and got it screwed. It went in and my smallest sprocket is back. Thanks guys anyway.

You've already solved your problem, but here is a very good source for a complete set of instructions on how t set-up and tune your rear dérailleur: http://www.parktool.com/repair_help/FAQrindx.shtml

Thanks Davet, mine was a problem of lack of common sense. It was not that I had no access to servicing instructions. However, those parktools maintainence instructions are real good, with all the diagrams. Great one, thanks a lot. I'll be adding it to my favourites.