IDE won't compile or download

For some reason, the IDE won't compile or download anything including sample sketches... I am switching between a Mega and an Uno... even if I download another copy of the IDE, it still won't compile even the Blink program... I used to work, but maybe I changed something and now it doesn't work on any program. Please tell me what to do... I am identifying the board and properly... help!

When you encounter an error you’ll see a button on the right side of the orange bar “Copy error messages”. Click that button. Paste the error in a message here USING CODE TAGS (</> button on the toolbar).

Hi,
Welcome to the forum.

Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.

Thanks… Tom… :slight_smile: