MacBook wont turn on at all

So I'm sure this final outcome is entirely my fault, but it didn't start out that way...

The backlight started playing up, firstly after I left the MacBook open for a while and the screen went to sleep then when I came back to it, I usually move the mouse to reactivate the screen but nothing worked. I could just about see that my programs were still open, but there wasn't enough light to do anything. I rebooted and it worked, that time.

Next, when I came to open the MacBook up in the morning (I've never shut down properly - usually just close the lid at night, so I can charge my iPhone through it due to lack of plug space) the screen didn't light up. It never really did after that, but I found that if I closed it and turned it round and upside down and stuff then opened it, it often worked. So I figured it was a loose cable issue. So I ordered a new invertor cable and (following the excellent guide here) installed it. It made no difference at all - no better and no worse. I reset the smc and pram - no change.

I then got fed up with the backlight only working sometimes and opened it up again to see if I could see anything obvious wrong. I thought I'd give it a go removing the squidgy foam from on top of the invertor cable thinking "how much worse can it get?" After putting macbook back together, it wouldn't turn on at all. I opened it up and put the foam back, but obviously that hadn't really had an effect.

So now MacBook wont turn on at all. No noise. Nothing. Now all this happened after I updated the os, but I'm sure that's just a coincidence.

I have an appointment to take it to the Genius Bar next week, but not being able to turn it on, I can't back up my hard drive and I have some irreplaceable things on there (plus some stuff that I dont really want them seeing)...

I have no idea what I've done, but clearly something. Any suggestions of wires to check/replace greatly appreciated.

Apologies for rambling...