I started using my bike again after i got back from vacation only to notice that it wouldn't shift into 1st gear unless i shifted into 3rd and then down to first again...does anyone know what the problem is that is causing this or how to fix it?

I would fully clean and lubricate your chain, as well as realigning your derailer and making sure the cable is tensioned properly.

Sounds like cable stretch. Turn your barrel adjusters at your shifters (little knob thingies where the cable comes out of the shifter) out counter clockwise in 1/2 turn increments with test rides in between to see if that helps. Shouldn't require more than 1.5 turns.

Also as JasBike said, lube the chain as well!

L8R

um...i tried what u said a2psyklnut and it still didnt work...any other suggestions...btw i just got this bike back from the bike shop again after ure suggestion didnt work and the guy said it was fixed yet it still doesnt work...

When was the last time you change the cassette/chain? If you changed one but not the other, the teeth might not be lined up.

that just confused me more...i didnt change either....i dont even know what a cassette is ....isnt that the thing u stick in a tape player and it plays music?

That answer my question to some degree. Your cassette and chain might be badly worn. The teeth on the cassette might be fubar and the chain might be stretched. (look on the rear wheel...there is a thing with buttloads of teeth...thats the cassette)

you might need to get these changed to fix your problem