Have had exactly the same problem with my Macbook 7,1 (Pro 13 inch unibody 2010).
48 hours ago, my MBP stopped booting after a firmware EFI upgrade. Right after the apple logo appeared after booting, a kernel panic was triggered and all further boot processes stopped. So I decided to do a major rehaul, replaced the HDD, took out the optibay for an SSD and upgraded my RAM to 8 GB thinking it might be faulty. The mechanic who helped me also said there was a problem with my hdd sata cable connecting it to the logic board so replaced that too. Last night I had the same problem recurring.
Got sick of it and tried an experiment, removed one (4GB) RAM slot - the one on the top - and tried booting it up again. The MBP works fine so far, but clearly sluggish and the smooth effects/transitions typical of OS X are now jarred.
I have the same question as Deep: Is it healthy running your Mac on just one RAM? Any long term problems? Can it handle SSDs?
'''Background:'''''italic text''
A year ago, 15 days after my warranty expired, the MBP gave 3 beeps everytime I switched on the comp and refused to turn on. I took it to the Mac "genius" guys and they said $1050 to replace the logic board, just to be "sure that it's nothing else wrong". I asked them to go fly a kite and instead tried my hand with an idiot in Singapore who said he was a certified Mac mechanic. Paid him $450 and still had no improvement after he kept it with him for 2 months citing "complex" issues. I got sick and tired of it all and threw the Mac in a box, generally cursing my luck and swearing at Mr Jobs.
A year later, a week ago to be precise, I just randomly opened it up and switched it on and it was bloody perfect for 5 days. Nothing went wrong, snappy performance, all apps were fast. Mr Mav was happy. And then when I updated software, came the grey screen of death "You need to restart your computer" kernel panic.