Stuck on Start Up Apple logo screen with 50% progress bar, tried everything. Please help!

Hi Everyone. I would really appreciate any advice you could offer me to help me fix my laptop. I have a Macbook Pro Mid-2010 2.4 GHz Core 2 Duo, running OS X Yosemite. About a year ago, it started lagging a lot, so replaced the HDD with a Samsung 850 EVO 120GB 2.5-Inch SATA III Internal SSD. It has been working much better since.

A few days ago, I bought a Google Chromecast and had set it up with my MBP. Afterwards, it started to lag and I noticed there were apps in Launchpad that I had never downloaded (Google Drive, Gmail, Youtube, etc). I could not delete these apps or drag them to the Trash. Concerned, I decided to back up my files to a USB stick and re-install the OS X.

However, when booting up the MBP, it becomes stuck on the Apple logo screen, with the progress bar never going beyond 50%. (Picture: http://postimg.org/image/66qh6x633/)

What I've tried:

PHASE 1 (Before Reformatting)

- Safe Mode: Pressed Power button and held down Shift. Hit or miss, worked 1-2 times, but when I reboot, becomes stuck at the Apple logo again.

- Reinstall OS X: CMD+R; after 15-20 mins gets to OS X Utilities Screen; Reinstalled OS X Yosemite; 7 hours to reinstall - but when the mbp restarts to complete the installation, it becomes stuck at the Apple logo again.

- Reformatting: CMD+R; 15-20 mins gets to OS X Utilities Screen (multiple reboots to work); Select Repair for all disks/drives (Samsung SSD, Recovery HD). Output said both are fine; Select Erase for Recovery HD. When that was done, I tried to reinstall OS X Yosemite, but the MBP suddenly shut off. When I turned it on again, it went back to being stuck on the Apple logo loading screen. Attempted reboot 15+ times, but same result everytime.

PHASE 2 (After Reformatting).

- Power -> CMD+R = stuck at Apple logo screen with 50% progress bar

- Power -> Option = shows 2 drive and Wi-Fi box (Pic: http://postimg.org/image/58qi2j1vl/); Have tried all combinations, but regardless, still becomes stuck on the Apple logo screen at 50% progress, after leaving it on for an hour, I sudden hear "To use English as the main language...", but the screen is still stuck. I left it on for 36 hours once and nothing changed

- Power -> Shift = Error (Pic: http://postimg.org/image/tahklsvy1/); Keep rebooting or shows another error (Pic: http://postimg.org/image/thstc6b59/) then rebooting. Never goes through.

Other Things Tried:

- Reset PRAM: When MBP restarts, becomes stuck at Apple logo screen, 50% progress bar

- Reset SMC: Stuck on Apple logo screen for a long time, and then screen turns off, but the laptop is still on. When I press Caps Lock, the indicator light turns on. Also, after some more time, I again hear "To use English as ...." even though the screen is off. Regardless of what I press, it does not wake the screen.

Note:

-The bottom of the laptop feels warm/hot (may be from battery), but I don't hear the disk moving.

I am desperately trying to save my mbp because I cannot get a new one for a few months. Any advice/help is greatly appreciated!.Thank you so much!!!!

P.S.: I'm not too computer savvy, so please use everyday terms/non-tech terms when possible, thanks!