Failure to boot after re-applying thermal paste

Hello,

My late 2011 MacBook Pro won't boot as it stays stuck on the white screen with the Apple logo. Shortly after displaying the Apple logo, it has the grey spiral going on forever. Sometimes, it has an empty progress bar pop up.

I took apart the Macbook to apply thermal paste using this guide:

MacBook Pro 13" Unibody Late 2011 Heat Sink Replacement

I have reset the NVRAM with no luck. I was able to get to the Repair option for the Hard Disk and the tool said there was no problem with the partition.

Right now, I am running an extended check using Apple Hardware Test (the standard test returned no errors).

Is my Macbook doomed forever? Any advice would be deeply appreciated.

EDIT: MORE INFORMATION PROVIDED (02/17/15)

Here's some more detailed information:

1) We re-applied thermal paste to the heat sink following instruction guides on iFixit.com for Mid 2010 MacBooks. Halfway through dissembling, we found out via the serial no. checker on Apple's website that it was actually a Late 2011 model.

2) I removed the battery during disassembling, not knowing that the computer was still technically on. After we thought we put everything back together, we pressed the power button and the MacBook turned on just fine. I was running random applications and testing functionality (Skype, Chrome, YouTube, Word, etc.). Everything was working. I installed Temperature Monitor (a hardware temperature gauge app that has been discontinued by the developer). I then tried turning off the computer but nothing would happen. I would try to restart, shut down, etc. and nothing would be responsive. It would just stay on the desktop, but no rotating wheel appeared.

I had to override shut down by pressing down on the power key for 10 seconds. Upon powering up again, the MacBook is stuck on the white logo screen with a spinning circle underneath. Sometimes, an empty progress bar shows up. The MacBook seems to be stuck at this screen.

3) I eventually discover that I did not plug in the fan cable and battery indicator cable upon re-assembling everything. So, I removed the logic board again (cause the battery indicator cable was stuck/wedged underneath) and made sure everything was plugged in.

I tried turning it on, but the same problem persisted--stuck on the white screen.

4) I tried resetting the NVRAM (Option+Command+P+R) with no luck. I tried rebooting into safe made (holding the Shift key while powering up) with no luck--it seems to stay stuck on the white screen with a rotating circle.

I was able to get into the System/Hard Drive repair mode (Command+R). I ran a repair operation on the drive that contains the OS (named "Big Mac"). It said that certain sectors had errors like 748 should be 762 or something like that (not exact). However, the main error seemed to occur during a Sibling Link check.

It would try to rebuild Catalog B-Tree, but ultimately says that it's not repairable.

I would then try booting into Single User Mode (Command+S). I tried to

"fsck -fy" but the same issue would persist about invalid sibling links and attempting to rebuild catalog B-tree.

5) I tried making a backup/restoring the main drive to an external USB drive using the Hard Drive repair tool. For some reason I can't specifically recall, it couldn't.

6) I ran a Hardware Test/Check using whatever tool accessible on boot-up. I ran both a Standard and Extensive test--with no errors returned. I'm not sure what this means--just providing as much info as I can.

That is pretty much the extent to which I've tried to fix the stuck white screen issue. Here are some suggestions on what could be done next (according to my research):

- Rebuild/repair the Catalog B-Tree and other Hard Drive structures using an external Mac OS X CD/flash drive boot.

- Buy a new Hard Drive ribbon cable (as suggested by someone on the iFixit forum because the Late 2011 models tend to have faulty cables)

Hope this was helpful.