Hi, I'm Peter, You may have your chain adjustment too tight. When you adjust the chain you should have it loose enough to where you can pick the chain up and there will be enough slack to where the chain guide that runs in the grove of the bar will be just a little ways down in the grove where you picked it up. If you can't lift the chain up with your fingers to do this it is too tight if you do this and the chain guide comes completely out of the groove then it is too loose. Make sure your chain brake is off also when you try to start the engine. I also pour a little chain oil on the chain and bar before I start it to prevent need less start up wear.
Hope this helps. Peter

Hi Ian:
Hopefully you've just got the chain safety brake set.
Try yanking REALLY ******* the guard, pulling it back toward the upper handle.
Reply as a COMMENT to this post.
I'll try to help.
Cheers