Help! - No power on B+ but GPIO power is fine

[archieroques]

I've just desoldered the USB ports on a pi B+. I had desoldered the ethernet some days ago, and it worked fine. I tested it without the USBs and nothing happened, except my DPI screen attached to an Adafruit KIPPAH glowed white, as it does just before booting normally. No power lights are on.

Then, I noticed that the capacitor C97 came desoldered by accident. I read that this wasn't needed, but I reattached it anyway.

Same thing still - the LCD lights up (I checked the GPIO voltage - it's at 4.3V), but no joy. I also checked the USB port voltage pins, and nothing is going to them.

Have I fried something? I really hope I haven't, because I need this pi for an urgent project!
Thanks.

EDIT: I've just done some continuity tests, and found that two USB pins are shorted together (luckily 2*5V ones), and these are both shorted to the ground plane. There is some black stuff stuck to the board, which seems to be plasticy at first, won't come off with chemicals or picking with tweezers, and I think it might be flux or something. Anyhow, it's conductive, I think. Will shorting 5V to the ground plane have bricked my pi?

[klricks]

GPIO power is not fine at 4.3V......

I would get a new RPi and keep the soldering iron well away from it.
It is difficult to remove 'thru hole' parts using only soldering iron without damaging things. Even with proper de-soldering tools sometimes things get damaged.

The 5V lines in the USB ports are controlled by a chip (U13) and and not turned on until well into the boot process. You can't draw any conclusions by making resistance measurements unless maybe you compare to a different working RPi.