stopped working

New at arduino world …had uno working for the whole day, but it stopped working …
It writes - the board is not selected, But in Tools/Board there is no options …
Arduino is noted in my device manager …
I do not know what to do…

PS. I read troubleshooting and nothing seems to fit my problem: No Arduino pins are connected to anything yet I have Windows 7 Restarted computer couple of times and reconnected USB in different orders I updated drivers at COM ... there is not problem here as well When I run Arduino, I have a message at the bottom "null on COM" Power and Pib 13 are blinking as suppose to when I connect to power and Bootloader is on the board (used reset button)

I think I have the same problem as http://arduino.cc/forum/index.php/topic,116107.0.html

karan-dash: But in Tools/Board there is no options ....

That indicates the Arduino IDE installation may be corrupt. Try removing and reinstalling.

Does your board pass or fail this test... http://arduino.cc/forum/index.php/topic,73748.0.html

I solved the problem .... it is embarrassing to admit what i did ... relocated hardware directory "Hardware" while in the installation by mistake when my computer froze ... accidentally clicked on something that I should not have ... I kept my window for file locations open I removed driver and installed it again and it did not change anything.