OS X Yosemite won't let my computer turn on

Question

So here's the backstory: I just updated to Yosemite yesterday and after downloading and updating it everything was fine, I got the new layout of the doc etc, but then it told me I needed to update iPhoto and other applications so I did. Eventually my computer turned off and then went to the light gray screen with the Apple logo and a progress bar that only went to about half way then stopped. After 5 hours it was still on that screen. I had to "Command+Option+P+R" it to get it to crash and come back.
Now its working fine, a little slow, but here's the real problem now:
I was watching Netflix on my laptop, not connected to a powersource, and of course I was multi-tasking and cleaning as Netflix was playing so my laptop eventually died and I thought, "Okay, I'll just plug in the charger and turn it back on." Nope.
It was then stuck on the light gray screen with the progress bar and I had to crash it again to make it come back to the home screen with the doc.
Basically, if I ever want to use my computer I can't have it lose power. How can I fix this? Please help!

Answer 1

Uninstall CleanMyMac - get rid of it.
Reinstalling OS X Without Erasing the Drive
Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
Reinstalling OS X Without Erasing the Drive
Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.
When the recovery menu appears select Disk Utility and press the Continue button. After Disk Utility loads select the Macintosh HD entry from the the left side list.  Click on the First Aid tab, then click on the Repair Disk button. If Disk Utility reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit Disk Utility and return to the main menu.
Reinstall OS X: Select Reinstall OS X and click on the Continue button.
Download and install the OS X Yosemite 10.10.3 Combo Update.
Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.
Alternatively, see:
Reinstall OS X Without Erasing the Drive
Choose the version you have installed now:
OS X Yosemite- Reinstall OS X
OS X Mavericks- Reinstall OS X
OS X Mountain Lion- Reinstall OS X
OS X Lion- Reinstall Mac OS X
     Note: You will need an active Internet connection. I suggest using Ethernet
                 if possible because it is three times faster than wireless.