My cooling fan is not cutting in on my bmw z3, i know the fan working fine so i suspect the relay /fuze has failed what it look like

fan electronics start at the sensor in the cooling system, and sends a signal to the ECM which in turn closes a relay and turns on the fan/s
There are 2 fuses in the system. one for the power to the sensor and one for the power through the relay
I suggest an accredited auto electrician with experience on your vehicle to quickly find the problem point.

You can drive the car ,but you may experience some handling issues and noise that you normally would not hear. Try to get it fixed as soon as possible to keep from creating other problems in the drive train components.

Jump the switch with a paperclip to see if fan operates. If it does replace switch. If not jump power to fan, if it does not operate then repalce fan. Also check fuses and far relay

The car has a Body control moduel that controls the windows, have it scanned to see what is going on with the windows.

Suspect #1 - air in cooling system. These can require several bleeding attempts to get all the air out. If the overflow reservoir is old and cracked inside, it will keep getting air back into the system.
Suspect #2 - radiator plugged internally with mineral deposits from hard water or silicates from using the wrong coolant. Does the radiator feel hot all over when the car is hot?
Suspect #3 - radiator plugged externally with organic material or the hair from the long haired cat that sleeps in your garage. Put a light behind the radiator and see how well you can see through it from the front grill.
Suspect #4 - failed fan clutch and/or failed electric fan. Does the overheating happen on the highway, or only when stopped or moving slowly? Does the electric fan kick on whenever the air conditioning compressor kicks on? The most common failure point on the electric fan is the relay.
A defective new thermostat is possible but unlikely.

Either head gasket or air in the cooling system or the aux electic fan is not coming on.

I too had similar problem when replacing the thermostat on my Z3. My advice is top up with more coolant and check the level.

check your fuzes, and relays for those circuits... for detailed info on this you owners manual will be a helpful guide.

In the fan circuit...You have a temp switch screwed on the radiator, a fuze and a relay in the fuze box plus a fan.  Swap the relay with another relay, replace the fuze.  The other fan should come on when the a/c is turned on.  If you fix the fans and it still overheats, you may have a BLOWN HEAD GASKET.  ALSO ARE YOU BLEEDING THE AIR FROM THE SYSTEM?  DO YOU SMELL EXHAUST IN THE COOLANT?   

This used to happen to my car and it was the automatic choke not kicking in .....old cars had a pull out choke but inour days this is a thing of the past