What should i do if my computer won't turn on but i hear the fan noise?

Hello JayaSharma,

It sounds like you can hear your MacBook Pro start up, but you do not see anything on the screen. I definitely understand your concern with this.

I found an article with steps to troubleshoot issues with displays. This article is for internal and external displays, so you can skip any steps referring to an external display. I recommend reviewing the full article, but this step specifically stands out to me:

Reset the system

You can reset the Mac's parameter RAM and SMC.

You can find the full article here:

Apple computers: Troubleshooting issues with video on internal or external displays

http://support.apple.com/kb/ht1573

Thank you for posting in the Apple Support Communities.

Best,

Sheila M.

Those are symptoms of a faulty dispaly, display connection or a GPU problem. The best option is a visit to an Apple store genius bar for a proper diagnosis.

Ciao.