NEED HELP MBP 15" (early 2008 model)

[meandmymac]

I need help! I have had problems with my mac since march this year. he just turned off and never turned on again. the technician said that its the logic board and that i have to replace it myself. After a while i finally found this guy in johannesburg (i am in botswana) who could sell me a logic bioard for an affordable price (the mac shops wanted 1000$ for the new board) - so the first one came and was DOA; then i sent my MBP to johannesburg, got it back, and it worked; for 10 days - that day i shut it down and took it to a friends house (it was the first trip since i got it back) i tried to turn it on and could hear hard drive and CD turning on and the white light went on but the screen stayed dead. so i took it to johannesburg, got a new logic board and it worked, for 9 days! i had it unplugged to drain the battery and it went black; so i connected it, waited a minute or two and turned it on again, or well i tried, i pressed space bar, heard it go on, but no screen. after a while i cold started it and same thing no chime black screen, but harddrive is spinning and light is on... since the beginning of March i had my MBP working for a total of 19days! it is driving me nuts... what kills logic boards??? it is my fault or did they give me bad logic boards (he claims he gave me 3 brand new boards) - what should i do? i need my MBP for work!