wow...."check the solder"? "loose handlebars"? "little spikey things"?
What are you people smoking?
You have a broken/frozen freewheel or free hub. The mechanism that connects the gears on the wheel to the hub is a ratchet system with spring loaded pawls. The pawls inside the ratchet have either broken off or are stuck so they don't engage. It's possible that , if it's a freehub, the retainer nut has come loose and the freehub body has slipped out of the wheel hub, but it isn't likely.
If it's a freehub, You need a new wheel. If the pawls are broken, they can't be fixed. If they are frozen, you need special tools to disassemble the freehub body, and there's no guarantee you'll be able to get them clean of rust and crap so that it doesn't happen again. If the retaining nut has come loose, it's likely that the pawls and springs have fallen out.
If it's a freewheel, you may be able to get away with replacing it. but it's possible that the freewheel is frozen to the hub as well, and you'll never get it off. So you'll need a new wheel then as well.
Even if it's just a broken freewheel, you need special tools to get it off, and just hope it isn't a suntour two prong style - those _never_ come off.
Take it to a bike shop. Someone needs to actually see this to diagnose it properly. Or you could just change the handlebars and hope for the best (wow.....)