I have a MacBook Pro 13", Core i5, Summer 2012 model. It's not even three months old but it exhibits a weird issue when I open the lid. I hardly ever shut down my Mac since I prefer to put it into sleep mode by closing the lid. Sometimes, for no reason & discernible cause, when I open the lid it might show the lock screen for me to input my password as it would do normally and then turn itself off. The light on the front besides the IR receiver keeps on flashing indicating that it's in sleep mode. Other times it won't turn on altogether without my intervention. I have to wait a couple of seconds before I try to press any key on the machine and see if it snaps it wake for me to resume using the computer. I have contacted AppleCare and followed what the advisor told me, first resetting the SMC & when that didn't work reinstalled the OS, to no avail. I am running the latest version of OS X Mountain Lion at 10.8.3 It's infrequent enough that I don't really mind but I am really curious as to what it is that it's happening ? Any ideas ? 
