My Audi A4, will not allow me to put car in gear with clutch depressed and engine running If I switch of engine I can engage gears easily. If I place in reverse and switch on engine with clutch down the car slowly start to move backwards. I susect clutch is not being disenaged. Where can I checj the clutch fluid as I can only find brake and power steering.

I am assuming this is a manual shift. Have you checked the fluid level in trans? Tried draining and replacing fluid? Checked clutch adjustment?

Agreed. The clutch disk is likely worn. The pressure plate is self adjusting so there is no adjustment available on stock Audi pressure plates or indeed in most pressure plates.

Another possible cause is a leaking rear main engine seal that is allowing engine oil to seep and then be thrown around the bell housing and work its way onto the flywheel/clutch/pressure plate.

Test you clutch in 3-4 gear acceleration from a slow speed...if the engine speed flares faster than the car accelerates, you have a worn/bad clutch.

Check the following:
- Thrust bearing, clutch.
TEST: Pull up the hand brake. Start the engine and let it at idle speed.
Depress the clutch pedal, put the car in 1st gear, while keeping the clutch pedal depressed. If the gear lever hesitates or produce any abnormal noise, replace the clutch thrust bearing.
- If the gear lever shifts smoothly, clean the throttle body, idle air control valve and perform idle speed learn learn procedure.
- Check the valve clearance.

lubricate clutch pedal at pivot points

transmission synchronizers most common cause of transmisson noise in certain gears, and not others, might want to check the gear oil level. Transmission rebuild required. To read about them and what they actually do, then here is a good read:
When you shift gears in your standard shift car, you move a rod that moves a fork that engages the gear. Depending which gear you're shifting to, a different fork does the job. The fork moves the collar to the desired gear, and dog teeth on the collar mesh up with holes on the gear in order to engage it. You engage reverse gear through a separate, small idler gear. The reverse gear always turns in the opposite direction of the other (forward) gears.
In years past, double-clutching was common in order to disengage a gear, allow the collar and next gear to reach the same speed, and then to engage the new gear. To double-clutch shift, you pushed the clutch pedal to free the engine from the transmission. Then the collar moved into neutral. You released the clutch and revved the engine to get it to the right rpm value for the next gear so the collar and the next gear spun at the same rate to allow the dog teeth to engage the gear. When the engine hit the right speed, you depressed the clutch again in order to lock the collar into place on the next gear.
Modern cars use synchronizers in order to avoid the need for double-clutching. A synchronizer, or "synchro," lets the collar and gear synchronize their speeds while they're already in contact but before the dog teeth engage. Each manufacturer's synchro is slightly different than the others, but the basic idea is the same. For instance, a cone on one gear will fit into a cone-shaped depression on the collar. The gear and collar synchronize their speeds thanks to the friction between the cone and collar. Then the outer part of the collar moves out of the way so that the gear can be engaged by the dog teeth.

Engaging in the top third of pedal travel isn't unusual.

Clutch drag can be caused by a worn or broken diaphragm, damaged pressure plate, worn or damaged withdrawal mechanism or contamination of the driven plate, among other things...
There are two other causes of clutch drag worth considering - rusted or damaged first motion shaft splines or a bad clutch pilot bearing, if fitted.

In all cases the transmission will have to be removed for access.

if you put your foot on the clutch all the way down,and then try ALL the gears when stopped.if they engage,without applying any force,then its the gearbox,possibly the baulk ring.

Do you mean with the engine off? If so, that is normal. The clutch just allows you to disconnect from engine when it running. With the clutch released and engine running the gears are spinning all the time. When in neutral, the chain of gears to the final drive is incomplete. When you engage a gear you are completing a chain of gear connections to the wheels. If engine is running, you will grind gears untill you press clutch, making a temporary break in the chain, allowing the gears to stop spinning and you to engage one.

You can infact use 1st gear as a kind of parking brake as it holds the car from rolling (in most cases) , with engine OFF, - BUT this is not advised as the only parking brake.

the transmission needs to be taken apart and have the second gear synchro replaced. i would start with just have BG sychro shift put in at a local shop that sells BG. that will help with the problem.

Thanks I got the solution it was fixed this morning. One of the gear links was loose and out of place just at the gearbox level