Handlebar of my bike will not bolt onto the front forks
Sounds like a quill stem, something like this:



That wedge bit at the bottom sounds like its come unscrewed completely.  Take the stem out, and look down the hole.  If you see a lot of light, then you've dropped the wedge and its gone.

If there's only a little light coming through the bolt hole in the wedge, then flip the bike, take the front wheel off, and any front mudguard, and poke the long bolt up from below.  The wedge should fall out the top.  

Once you have a wedge again, loosely bolt it to the stem with the long bolt as pictured, insert into the steerer tube, and reassemble.