Macbook booting with startup noise but no screen activity!

Update your system with good antivirus and restart your Mac.
Check your Startup Items and delete if not required.
Clean up in System Preferences.
try to Upgrade your Ram for memory boost up
if not helpful and need more than follow https://www.apple.com/in/support/ .

Is this a trick question? There is no "DOS mode" on a MacBook Pro.
Do you have WIndows installed as part of Boot Camp, and your machine is booting into Windows? To boot back into the Mac, either use the Boot Camp control panel in Windows, or hold down the Option key after you hear the startup chime and select the OS X partition to boot from.

does it have ram inside. safe boot is a must. it took me 5hours to hack g4ibook 4 my 1rst time fscky aka command line. or on your other mac do superduper app.

The issue is with the software.Boot the system with installation media and go to disk utility and repair the file permission.This can solv the issue.If still the issue persist.Then go ahed and format the drive and re install the software

it can be the cooling system, but you will have to show your machne to a reparator.

Laptop is looking for a bootup device. Insert your mac operating sustem disc and boot from the disc, then select disc utility from the top header listing and select verify disc, let the system check run and reboot.

Boot from the original system DVD and try a repair from there

have you gone into system preferences/sound.input/output settings?
try making a free test call, and you can play around with all your settings that way...also helps to keep the volume turned down on your mac, and just adjust it using your headset.

try holding down the alt(option) key when starting up it should give you a list of startup options, it sounds like you dont have a astartup disk (an operating system) installed.

you are having main-board issues and possible harddrive issue.
but the mainboard can cause drive failures your info might be fine,The blue screen indicates a board error(memory usually)