I2c LCD not working at all

Hi
Just encountered problem with i2c interface all was working fine LCD displaying ect was running from usb port all fine for about 2hrs switched it off and now no light on i2c and nothing on LCD no back light totally dead running Arduino Uno and screen only project still loads on Uno and compiles just nothing on screen does anyone have a clue has i2c blown something have tried to connect pos and grd to a separate battery but it's totally dead the screen an i2c came as one component when bought 2 months ago
Colin

Hi
Connected up spare i2c interface to battery and that lit up tried the original and it's dead but did touch either side of the main chip and the light on i2c lit up so not sure wot has gone on has anyone had similar issues with these
Colin