USB port not working anymore

Hi,
have been playing around with my arduino mega 1280 and a 24vpower supply. (24v + ULN2003 + 6LEDs on PIN 13 and 2 12vFanson PIN 10)
However, somehow my USB is not working anymore - my board will not be recognized from the software so I cannot upload any sketch.
What I noticed: power is still working via USB: three leds are lighting: RX, TX and PWR.

Any idea what could have happened? Fixable?

Thx

Can you please draw a diagram of how you had your hardware connected? Your ultra + condensed + single + line description isn't descriptive enough.