CPU Locked at 1,60 GHZ

Hello

So a few months ago this imac started showing bars and signs of GPU failure…it then completely failed and it became very slow and unusable.

I am not a pc repair technician or expert i mostly create music but , since i lack the cash i had to solve this issue .

after some reading and speaking with people they told me reflowing the GPU would bring it back to life ( maybe) so i tried it. With success! i disassembled this piece of crap , did the reflow on my oven, reassembled and voilá, computer all good!

Now, before all this the HDD failed as well and i replaced it with an SSD …tearing the RGT SKIN sensor cable in the process…it was all good the computer kept working normally…

so for my problem…after doing the reflow which meant removing the logic board and removing the CPU and GPU heat sink and replacing the thermal paste i now have the CPU clock locked at 1,60GHZ…i also have the RGT SKIN cable not connected to the board since i the connector in the logic board is damaged and i can’t connect there, it’s weird it’s like it’s glued and i can’t take the lid of ( trust e i tried and broke it even more)

so after some more reading another person had this issue and the post says replacing the backlight LED board fixes it…i find it weird since it was working before without this cable connected…i went to store they say an “ Apple Machine” has to be used to set the firmware clock? is this true? no work around it ? they say the computer has been tampered by the user and they do not accept it… so im stuck with a working GPU and a CPU at 1,60ghz…ARRRRRRRRR! anyone can help ? Apparently OpenFirmware does not work as well…no app that allows to configure CPU clock speed ? Thanks in advance