Arduino not detected by computer..

I have Uno R3 and both led power indicator and Led on pin no :confused: 13 glowing contineously.Computer is also not detecting device.Is this board damaged???

Try the Loopback Test, it's one of the Sticky posts at the top of this forum. Perhaps you just have a PC driver problem.

The power led (green) should to light continuously. L depends on pin 13 state. Is it original Arduino? Did it worked previously? The computer is detecting USB/serial converter. If not, it can be damaged, wrong connection (USB cable) or there is firmware missing or problem with the driver on PC.

It was working before that and its original Arduino.I was programming LED strips with UCS1903.i connected 12v power supply and taken 12v from Vin pin for LED strips..But after sometime r stopped working and both Leds get on and and computer not detecting the board...Its not showing in device manager list also.. :(

www.bestlightingbuy.com/pdf/UCS1903%20datasheet.pdf

Looks like a WS2811. Does the loopback test still work? Do any components on the board feel really hot? You may have damaged the 5V regulator, or the reverse polarity protection fuse if you were pulling a lot of current thru it. The LEDs should have just been powered in parallel with the barrel jack feed, and not come from Vin.

Computer is not detecting board..I tried on different PC's..And M7 diode was very hot at that time when this happen to board..

Ok, you may need to replace M7 then, it shouldn't be hot. Measure the physical size of your part, I am sure one of these will be a suitable replacement http://www.digikey.com/product-search/en/discrete-semiconductor-products/diodes-rectifiers-single/1376383?FV=1140003%2C180004b%2Ce48000e%2C1f140000%2Cfff40015%2Cfff8007f&mnonly=0&newproducts=0&ColumnSort=1000011&page=1&stock=1&pbfree=0&rohs=0&k=diode&quantity=&ptm=0&fid=0&pageSize=25&pkeyword=diode

Is any other part hot?

Will it sort out the issue???Bcz connecting Arduino using USB to PC makes it ON but PC not detecting it..

If the USB is still supplying 5V power (measure from 5V/Gnd on the power header using a multimeter) the PWR LED turn on.

If the USB/Serial chip near the USB connector is dead, the Rx & Tx lights may turn on and stay on. Or they may be off.

If the 328P chip is dead, the L LED may be on, or off, but likely not blinking.

I checked the board with multimeter.M7 is ok but regulator AMS1117 5.0 shows short.And th voltage on VCC nad GND pin of Atmega328p is 3.68V.I removed Amtega328p from dip socket..After that L-LED shown off and start glowing gradually from low brightness to full brightness...

The L LED is driven by an op-amp. With no '328P, the input to the op-amp floats so the LED brightness will vary.

Need to find what's shorted. Could be the 5V regulator, could be the 3V regulator, could be a capacitor.

220 SMD resistor array between USB plug and MEGA16U2 is short...I think it burned out...is it cause???

https://www.arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf I believe those are 22 ohm resistors, yes, that could be a problem.