In theory, the pressing of certain keys could screw up a boot sequence, but the fact the keyboard worked before it was manipulated, means that it is likely a contact issue with that ribbon cable -- either it is inserted off angle, or poorly inserted; pull it out and clean it gently with the rubber end of a pencil, then try to insert it back in as straight as possible.
The keyboard itself it made cheaply with a "membrane" with 2 small carbonized rubber pads for each key; the keys have a "U-shaped" carbonized rubber piece that crosses the two contacts. Unfortunately the membrane uses a glue easily dissolved by alcohols, so one has to be gentle in cleaning it. Here you can rub with the eraser, but wipe with water.
The UK keyboard works like an American, but there are a few keys off. You can buy the stickers to put on them off idiotBay if you can't remember the differences.
