There may be a chain brake that you have to disengage. It would be a handle looking lever. You pull it toward you to disengage, push forward to engage.

If not that, then your air flow could be restricted by a clogged airfilter. Others may have different suggestions.

And on some saws it take a pretty good tug to get it off, try pushing it ahead first too make sure it's on then pull back, you should hear a snap when it comes off. Steve

doesn't appear to be the chain break, i checked that the other day when i was messing around with it the other day. any other suggestions?

many thanks in advance

I guess there could be a problem with the clutch but I would not know what those problems would be. I know what they do and how they operate (mostly) but I would not be good at troubleshooting them. I think they have a sheer key involved with them.

Does the engine accelerate when you blip the throttle? If it does not significantly change when you do blip it, then it is chain break or air supply (clogged filter, etc.) in my experience (there are probably other things that I don't know about). If the engine does accelerate normally, but no chain movement, then the power from the engine is not transferring to the chain. Part of that path is the clutch. I can visualize the other parts in that chain but I don't know all their proper names or more importantly how to fix them. I would have to take it to a shop at that point ;).