wheel and handle bar turning?

[double g]

I was on some trails today that were made for four wheelers so there was alot of stuff from downed trees and limbs from some recent storms. Needles to say riding was made difficult with all the stuff in the paths that would stop my forward motion going both up and down hills.  On two separate occasions one minor and one not so miner i bit it on the trails and my front tire would turn in a direction other than straight in front of my handle bars. On the first occasion i pulled out my allen wrenches and tighten the bolt as tight as it would go figuring it was just loose, but then it happened a second time, although they both happened on wrecks i a little concerned. I ride a 2011 diamond back outlook. Any experience or suggestions besides learn how to ride?

[Cereal_Killer]

When you say you "tightened the bolt", are you meaning the top cap bolt, the single bolt going through a coin shaped/sized disc?  The one on top of your stem?  All that does is set the load on the headset bearings.  Sounds like your stem pinch bolts are loose.  First, loosen/tighten the top cap till the stearing is snug, but with no play.  Not too tight.  Then, line up your stem with the front tire, and tighten the stem pince bolts.  That should take care of your problems. 
This website picture shows the different bolts and stuff if you're unsure. 
http://www.bikeradar.com/forums/viewtopic.php?f=40073&t=12689155

Hope that helps out. 

[double g]

Thanks for the pics. I took a look and I didn't see those bolts. Here is what the front of my bike looks like.

[double g]

Not sure what happened to the pics. I will try to repost them.

[nepbug]

Ok, from the pictures it shows you have a quill stem, not a threadless like Cereal_Killer was assuming.

So all you can do is either replace the stem with a different one if it is inherent to that stem (I'd recommend a Profile Designs BOA) or try to increase the friction down there.  If you go with a new stem, remember you need a 1 1/8" quill stem.

If you just want to try to add friction I would take out the stem (loosen the bolt you had tightened and then pull out the stem), clean it off and add some Ritchey, Finish-Line or some other brand Carbon Friction/Assembly Paste then put it all back together.

With a quill stem, each time it twists like that, then next time becomes easier so try to solve it as soon as you can.