New to cycling, gear problem on new mountain bike

Hi there

I've just bought a new basic mountain bike with 18 gears for commuting and I'm having some problems with the front gears. The rear gears are working fine but I cannot seem to get the front gears to move up from the lowest (smallest) cog and as a result I'm having to freewheel down even the slightest of slopes as I am unable to propel myself any faster than 6th gear - very frustrating. I've tried adjusting the cable tension and the screws, as well as the barrell adjuster, and nothing seems to have made a difference. As I bought it online I can't ask the shop to tune it up unfortnuately so unless I can do it myself I'll have to fork out for a shop to look at it.

Any advice would be gratefully received!

Thanks
E

Does the front derailleur move at all when you try to shift?

I have gotten home with a broken derailleur cable by simply moving it to the most versatile front chainring, then wedging a piece of wood into the derailleur so it couldn't snap back to low gear.