No power? wont rev above 3000

Have the codes read and repost. Could be a clogged catalytic converter.

You omitted to say whether petrol or diesel powered?

If the engine starts ok, sounds ok and runs fairly smoothly but is just down on power and revs it does suggest either a strangled intake or exhaust. Certainly these things should be checked and eliminated before moving on to more complex checks.
It is not unknown for intakes to pull in something like a plastic bag or for the catalyser to become blocked. I have also seen exhausts blockedby being bent by careless reversing into a high kerb.

Once those things have been eliminated it will be time to ensure the routine maintenance is up to date and competently carried out, a careful visual inspection of the engine compartment checking pipes, cables, wiring and connections. It would also be a good idea to ensure the valve timing is good and the fuel pressure and volume meets specification.

After the above preparation work it will be time to use a decent obd scanner and examine the live data as the next stage. Hopefully it will just be an old-fashioned simple blockage...