Just wondered if anyone knew what I did to get ms excel to select all cells from A1 to what ever cell I clicked on. Thought it was sticky keys but it was turned off. Clicked left mouse button and it moved cells then when I clicked other cells it started using that as a new ref point and selecting more cells from that. It sorted itself out with a reboot but I wanted to know for furture reference.

Check your SHIFT keys as it sounds like one of them is sticking, hence selecting all cells.

Just press the SHIFT key multiple times hard, also may be worth turning your keyboard upside down and banging it on the back to help remove any rubbish that has built up.

It also might be the computers "sticky keys". If you click shift 5 times in a row, it may be activated. To fix this go to Control Panel, then Accessibilty options, and disable sticky keys. Also, if you keep pressing shift 5 times, make sure you say no to sticky keys.