Harddrive/Motherboard Question- one of many (LoL)

I got my MBP in the summer of 2012 [Model No. A1278 13.3" i7 processor 2duo 2.4ghz 750gb (failed original internal harddrive)]

when it first failed, i brought it to apple and they said it would cost 750$ if they mailed it out (no details of work included), after some troubleshooting and research i thought my problem was the internal harddrive, so i went to best buy and had them install a 1tb internal replacement thinking my problem would be gone... that was not the case.

did i void my warranty by having geek squad do the work instead of apple?

i was running osx from my external firewire due to internal HD failure, but now my keyboard and trackpad failed. is my motherboard safe since i could use an external? a computer shop in San Fran told me that since i could use the usb, firewire, sd slot, etc that my motherboard was fine and that the problem was between the harddrive and the motherboard.

im an unemployed communications/visual arts student on a tight budget, i would like to avoid spending almost the cost of a new laptop to fix my old one, and im also not in the position to spend that kind of money right now. that being said, any helpful information would do wonders to my situation, and if this is not posted in the right section, or if its a repeat question, moderator please delete this.

Namaste.