I am using irf540n at first it works as expected +ve to gate close circuit and leds turns on -ve to gate open circuit but after a while it stays conductive no matter if I connect gate to +ve or -ve it just doesn't turn off although when I touch gate with finger it sometimes turned off and turned on as well and when I check it with multimeter Drain and Source is shorted even when there is no wire attached and Its just didn't happen with one mosfet but 6 show similar problem of which 2 of them works strangely and turns off when I applied +ve on gate and turns on +ve. At this point I'm so frustrated couldn't figure out why is this happening.
I'm using 5vdc from computer powersupply source is connected to ground drain is connected to led's negative with 220ohms resistor gate is directly connected to ground with 100ohms

 

Did you pull the gate back to ground or did you leave it floating ? If it is floating then the gate source capacitance of the mosfet will remain charged for quite a long time. This is probably the effect you are seeing.

Les.

 

Please post the schematic and label the details.

 

Place a resistor from gate to ground to discharge the fet. Please post a schematic.

 

need to discharge the gate.

 

Thanks for all the help, I was using faulty computer power supply which leaks ac voltages on 12v dc line which destroyed all mosfets connected to it