Urgent help. Stuck with black screen after el capitan installa

Try this first and report back.

Try safe mode if your Mac doesn't finish starting up - Apple Support

Can you boot into your Recovery Disk and try a verify and repair through Disk Utility. About OS X Recovery - Apple Support

Other things you may want to try are resetting the NVRAM, How to Reset NVRAM on your Mac - Apple Support

Or reset the SMC, Reset the System Management Controller (SMC) on your Mac - Apple Support

You could try to start up in single user mode or verbose mode and see if you can spot where the Mac is getting stuck

on start up. How to start up your Mac in single-user or verbose mode - Apple Support

As you mentioned before you were getting the beachball often so this may be an indicator the HD was on its way out

And upgrading it was the last straw, perhaps.

If nothing improves you might have to make a genius appointment at your nearest Apple Retail Store, if you have one.

Did you make a back up before doing the upgrade? Are you able to connect your Mac to another and then start up in target disc mode so you can copy your important files, OS X Mountain Lion: Transfer files between two computers using target disk mode, same procedure for El Capitan, but may not work depending on the state of your HD.

Seems like a dead disk to me. Especially when the Recovery Partition did not come up either.

Senoritalife wrote:

It worked after formatting disk and after restarting many times. How do I check if there is anything wrong with my disk ???

How full was your disk drive before reformatting it?

It may be that your disk was too stuffed to run the upgrade to completion - and the black screen may indicate the screen went into power saving/screen protection mode because of no action from keyboard or mouse (that indicates you are using the computer for time out clock restart).

Finder/Search preferences probably defaulted back to search everything - and that index build may be the cause of the slow startup.

I still have uneasy feelings about your disk. I really think it is dying.

Make backups immediately before doing anything else.

Then start DiskUtility and check the S.M.A.R.T status. if not good buy a new disk. If good it may still be dying.

There are some disk analysing apps to test further. But I do not expect anything else.

Apple Hardware Test doesn't catch everything, so even if it doesn't find a problem, you could have one.

Apple Hardware Test

Apple Hardware Test – Invoke and Interpret

Apple Hardware test – How to run and interpret (2)

Apple Hardware Test - Using

Apple Diagnostics – Computers introduced after June 2013

Apple Diagnostics: Reference codes

Senoritalife wrote:

Hi , I think you were right.

I formatted from external drive . Had no problem in formatting now and also took less amount of time.

Wheel of death did appear but lesser times comparatively . But a day before when I was doing some light activity on Mac - it suddenly shut down and it opens up to a flashing question mark page. Tried to verify , repair disk etc - but it does not detect the hard disk any more .

Somewhere I saw in Google , that this could also be due to faulty cable.

But since I am getting the circle of death at times and now this flashing question mark and disk not being detected - can I confirm that my disk is DEAD ?????

Yes, I think so.

Is the disk ever replaced? I suppose not. Thus the cable as cause is extremely unlikely.

But it is not a bad contact here, the issues you describe are exactly those of a dying, almost dead, disk.

Don't wait a second and make backups.

Then prepare yourself to have the disk replaced.