Screen shows circle with a line thru it? How do fix it

You can try resetting the pram. Command/Option/P/R keys at startup for three chimes. If this does not help. You will need to use disk utilities or do a reinstall. If you have Lion or newer, go to recovery using Command/R at startup. If you have an older operating system, you will need the install disk. In ether case, use disk utilities to repair the dive. If this does not work, Reinstall.

It would be helpful if you indicated the EXACT model/year MBP that you have and the OSX.

Ciao.

That means that your Mac can’t detect the operating system its running....

You will have to boot your mac in OS X recovery mode and try to fix the hard disk if its corrupted by going into Disk Utility.

Here, do this....OS X Recovery

Repairing a Mac Boot Disk with Disk Utility & OS X

• Reboot the Mac and hold down Command+R, or hold down OPTION
• Select “Recovery HD” at the boot menu
• At the Mac OS X Utilities screen, select “Disk Utility”
• Select the boot volume or partition from the left menu and click on the “Repair” tab
• Repair Disk is now possible, click on “Repair Disk” to repair the boot volume

Hope this helps....