Hi All, sorry for the rambling nature of this post.. lil' bit stuck! My mac runs 10.7.5 I bought new ram last weekend from Mr. Memory .com (kingston) 2xgb sticks. Initially I insrted them wrong, putting one stick on the different risers as i have never done it before and thought that's what it meant by matched pairs, it only showed up 1x2gb sticks on the scan and after i contacted them and found the right installation method I then had every running properly, along with 2gig more that I had previous making a total of 6gb. I then started to worry that trying the inital wrong combination might have had an adverse affect on my computer as I notcied an article saying that wrong placement of ram could do.. but it was running super fast for the first time in ages and I was happy.. However, last night I left my computer on as I was downloading something and when i came back and pressed the spacebar to stop the screensaver, the screensaver paused and the beachball started spinning.. and spinning etc. The only option was to turn off the computer via the power button. On trying to turn the computer back on , after showing the apple logo and the spinning gear it went to a white screen but went no further. I have Applejack installed so I started it using cmd+s and did an auto routine. I can't quite remember what but it seemed to stall on something that it hadn't previously. No joy.. Next, having looked in this forum and others I first tried a PRAM reset, and then a NVRAM reset (how do you know if this one works btw?) but still nothing. I then tried booting in Safe mode.. this worked. I looked around and couldn't see anything wrong but after restart no joy still.. Having booted the computer in safe mode I thought i'd test the ram using Tech Tool Pro 5 (althought a dialogue popped up saying it hadn't been tested on 10.7.5 yet...). All RAM passed the test. After that I tried testing the video memory - as soon as I did so Tech Tool quit unexpectedlly. Now, I have seen previous postings citing the video card as the issue - but as it said that tech tool hasn't been tested on 10.7.5 i don't know if this is a conincidence or not. I have saved the report if anyone thinks it would be of help, i'll post here. My graphics card is NVIDIA GeForce 7300 GT 256 MB. I then decided to try a diagnostics test by using cmd+d but it wouldn't work - just going to the white screen each time and hagning once more. And yes I did try the keyboard in another USB port. I have since noticed, and i'm not sure at what step it started doing this after, that just before the Apple logo appears at startup a grey folder with a question mark appears super briefly before.