Early 2011 MBP stuck on gray screen, verbose mode shows SMC error too

Hi!

I have and early 2011 MBP, running on OS 10.7.5 is continuously stuck at grey screen upon start-up.

I tried the steps as mentioned in Mac OS X: Gray screen appears during startup - Apple Support article apart from reinstalling OS X. The laptop started after every step, but then stopped again. I tried SMC update, that also worked for once, and on the second start up I ended up with a blue screen. During a later attempt, it worked again for a while, but ended with a distorted graphics after 15 mins. AHT (short version) doesn't show any hardware errors. Now the laptop doesn't go further than grey screen at all, and after a minute or so there's a heavy fan activity. The verbose mode also shows and SMC error, smc: : smcinithelper error: mmio regmap ==null - fall back to old smc mode (AHT Shows SMC version as 1.69f4)

What do you advise?