Nano NOT detecting via USB, but blue LED is on

My nano DID work for a brief period via a USB cable. was doing the simple trimpot / servo thing. After about 1min the LED went out and it stopped working. Process of elimination showed it was the servo which was causing the issue. Removed it, and the blue LED came back on, but it was dim.

The nano by itself on USB WONT detect, but the blue LED is on, although very dim. If i have a 12v ext power source, it does detect. and the LED is bright. With only USB, the yellow and red (TX / RX) leds flash about every 500ms and are also very dim. With BOTH plugged in (usb then 12v), blue stays on, and the other 3 flash about 3 or 4 times and then turn off.

I cant find a diagnostic on it. Its like its been shorted or the bootloader is not working properly. Is that the case ?-

It still "works" to some extent. If i turn the trimpot, the servo follows, but its on for 1000ms, then off for 1000ms. and RX/TX flash in that time like its waiting for something. Is there a way to scrub the entire thing and start again ? Ive tried another servo, exactly the same behavior. Any help or info would be much appreciated.