can not select gears when engine running

hi folks got a 52 plate freelander Serengeti I brought this car in august
fitted a new head gasket and new valves etc
finaly got it on the road 2 weeks ago engine running smooth everything seemed fine then wifey was driving to work when she started to have trouble getting gears.
she managed to get it on a car park I went over to see what was wrong .
so here is the problem I`m having when car is running can not get gears
when engine is off can select gears ok
there has been a new master and slave cylinders fitted by previous owner
clutch pedal can still be depressed but will not go into gear
thankyou in advance for your help

The clutch bracket may have failed. A common thing.

sounds like clutch ,get some one to check the slave is doing its job when you depress it as it may not be.

I had this problem recently - the arm the slave operates had stuck, and the slave bracket had bend. Spray with lots of WD40 where the arm enters gearbox, massage with clutch or tool. Check slave is moving when operating clutch. If not, check that master is still attached to clutch pedal. I changed master/slave also, it was sort of working, but had a small leak by the rod in the master, so in the end not enough fluid in the system, and it was sucking air on reverse travel. A way to check this, is to see if gear selection gets easier if you pump the clutch four-five times. Hope this helps.

thanyou all for advice given I will go and check everything out and get back too you all thnx

I had this a while ago and my master cylinder had failed. Replaced it with a cheap one but it needed constant topping up, as it turned out my slave had a leak. Replaced the whole lot with genuine parts, except the slave had to be replaced by the garage as the TD4 the slave is inside the gear box. That cost me £400 to replace and did the clutch kit at the same time.