ubuntu stuck in black screen after pressing power button. proceeds after any key press

ubuntu stuck in black screen after pressing power button. proceeds after
any key press

I was in 13.04 where suddenly one day, I started to get black screen after
pressing power button. it only proceeds if I press space or any other key.
I press space key now. Then it goes to boot ubuntu with the following.
then it enters into the welcome screen. I want to have a normal boot
process. I need help.
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