Arduino UNO Vin troubleshooting

Hi, I'm having some problems with the Vin supply. Actually I've never used it before, because I used to connect my arduino to the usb on the laptop. These days I was working on a project that requires 12 V and I built up my circuit as this one http://arduinoelettronica.files.wordpress.com/2012/03/rgb_lamp_circuit.png?w=627 When I connect the battery supply the project didn't work but status leds on arduino did. So I changed some connection and tried again with the supply. Then nothing was working at all! I thought I had burnt the microprocessor but when I connect it to the USB supply it does work (the leds too).. Instead when I put 12 V supply it doesn't work any more, I tried to measure the voltage on the jack and it's all right, it is 12 V. But Arduino doesn't seem to receive them! WHat should I do? Is there any troubleshooting?

With 12V connected, do you see 3.3V (or 5V?) on the VCC pin?
The promini regulator is only capable of 150mA, and much less when the RAW voltage is high. Altho your schematic wouldn’t suggest much current flow.
How are you connecting it to a USB supply?
Are there current limit resistors between the LED cathodes and the transistor collectors?

CrossRoads: With 12V connected, do you see 3.3V (or 5V?) on the VCC pin?

no i can't see any voltage there, it's 0 V.

How are you connecting it to a USB supply?

I'm connecting it with the usb port from my computer

Are there current limit resistors between the LED cathodes and the transistor collectors?

Do you mean the RGB out? My circuit is the same as that one in the pic :/

Sounds like your regulator is shot.