MacBook Pro 10.10.5 frozen on starting progress bar

For 2 days, my MacBook Pro 15" (early 2006) running the latest update (10.10.5) is stuck at the restart phase: grey screen with the apple and progress bar never goes beyond 30% and stays there forever.

I do hear the chimes before the progress bar page.

Sometimes, after a while, I get a grey empty screen and that's it.

I've tried the following (after turning it off)

starting:

- with (left) Shift+ Ctrl + power button to to reset SMC ( I get the stuck progress bar)

- with Shift + Ctrl + Option + power button (nothing happened)

- with Shift + power button (stuck progress bar)

- with Cmd + R + power button ( stuck progress bar)

not sure if related: Originally, the MacBook was hooked up to an apple Cinema Display and I used the display's power plug on the laptop but i noticed when this happened that the power plug color had switched to RED so I unplug all the cables coming from the display and all external drives as well.

Now the power plug is orange, but I can see the MacBook is fully charged, and it turns to GREEN only while I'm pressing the power button.

Once I release the power button, it goes back to ORANGE.

Please help!

thank you