MacBook Pro 15" 2008 boot loop issue

Hello everyone! I have an issue with my MBP 8.1 early 2008 15".

The other day as I was editing photos in Lightroom the screen hang and was sort of blinking, everything froze. This was with my Dell 24" display connected via DVI to the MacBook, as well as a external USB drive with TimeMachine and a bluetooth apple keyboard, all with the MBP closed. OS X is Yosemite with latest update. I have

When it froze and started blinking I did a forced restart by holding the Power button. The system rebooted, a gray screen appeared saying "Your system has rebooted after a serious problem" or something like that, rebooted again, the loading bar reaches about 1/3 and it reboots again, the error screen appears and then reboots again. Basically now it just reaches 1/3 to 1/2 ot the loading bar and reboots. It won't allow me to run diagnostics by pressing D. It will not boot the Recovery option, nor Safe Mode. By trying to boot Safe Mode, it again reaches 1/3 of the loading bar and I hear a voice asking whether I'd like to use English as a main language and to press Return, but the loading bar just stays there.

Tried resetting SMC and PRAM. I made a bootable USB with Yosemite and when it starts booting it, it reaches a gray screen with a "Prohibited/Not available" sign.

Since I have a Samsung SSD in it, I tried booting my old HDD in an USB enclosure with OS X and Bootcamp on it, but it won't see it.

I am thinking of opening the MacBook after work tonight to switch the SSD with the old HDD to see if that would make it load OS X. Also I will try with a friend's MBP to connect directly with FireWire in Target disk mode.

Any help will be much appreciated guys. I don't want to contact the local apple service. It's a last resort option. Last time they charged me 500 Euro for logic board replacement, and they are known of switching parts in machines, selling old Macs as new ones and what not.

 

True. If they tell me it's the logic board, that's the end of it. Was already thinking of getting a new Mac, but I wanted to wait for the new Intel CPU's in Retina MB's. And to save some cash for it...

 

Could be an option, yes. I don't have refurbished macs available in my country, but there are second hand of course. I'm afraid of video card failures again. I noticed there are some video card issues with MacBook Pro's from 2011 to 2013.