Bicycle Mechanics - Wheels not turning when I pedal!?!?

I've had my 21 speed Diamondback Insight One Hybrid Bike for about eight months now. I haven't used it for the past few months because of the weather. You guys on the East Coast know what I'm talking about. Just today I decided to bring the bike out for use cycling between classes at school. Lo and behold whenever I pedal, my wheels aren't turning and I fall off balance. That really impresses the girls.

My chain is catching the gears and they are turning but my back wheel is not engaging. I'm a relative novice at bike repair (I can take a wheel off though). What's going on and can I fix this on my own? Please help!

~Philip

The pawls in your freehub aren't engaging. First, try warming up the bike. If that doesn't work you'll need a new freehub. If you have the right tools (and a new freehub) you can change it yourself, but your Local Bike Shop may be the better part of valor.

Hopefully, you bought the bike new at a Diamondback dealer. The wheel will be covered for one year under warranty. If so, return the bike to the shop and if it is indeed a bad freehub body, you can expect them to replace the entire rear wheel for free under warranty.

The pawls in your freehub aren't engaging. First, try warming up the bike. If that doesn't work you'll need a new freehub. If you have the right tools (and a new freehub) you can change it yourself, but your Local Bike Shop may be the better part of valor.

21 speed Altus level bike is almost certainly a freewheel, not a freehub.
To the OP,some light oil dribbled in the gap between the part that rotates, and the part that's stationary when you spin the gears backward will likely solve the problem.
Worst case scenario, new freewheel, 15 bucks.

Or is the tire wedged into the stays? This can also prevent it from turning. Look.

21 speed Altus level bike is almost certainly a freewheel, not a freehub.
To the OP,some light oil dribbled in the gap between the part that rotates, and the part that's stationary when you spin the gears backward will likely solve the problem.
Worst case scenario, new freewheel, 15 bucks.

Incorrect. Freehub.

DMF and vredstein have nailed it. Since your bike doesn't have Shimano hubs, it's not likely to have a freehub body that's easily replaceable, but it might have one that's easily overhauled as an alternative. Even if you can't take your bike back to a Diamondback dealer, any shop in the northeast that knows what they're doing has seen this before and can fix it for you somehow.

Sidenote- I had this happen on my winter bike a few years ago, but it only only revealed itself once I had ridden halfway across the frozen lake. Studded tires but slippery boots... Not a good time.

Diamondback uses cheap Joytech hubs on base models that aren't too durable. If the bike is still under warranty, the shop should replace the wheel.

Here is the link to the Park Tool website for Freehub overhaul. http://parktool.com/repair/readhowto.asp?id=45

Incorrect. Freehub.
If you say so. I was a Diamondback dealer up to the 2008 model year, and any models I dealt with that were 21 (7) speed had freewheels. That said, Diamondback product line was somewhat different in Canada than the US.