where do i stand?

I bought a 2009 MBP 15" 2.4 just under a month ago, minus any additional apple care products or support, my machine was quite shaky from out of the box, a bit slow and kept getting caught in start up with the spinning dial (my girlfriend has a mac and said it seemed quite slow) so i installed 4gb crucial memory and a seagate 7200 500gb momentus drive but sadly this hasnt helped the situation and as i have tried to use the MBP more, more problems have arisen and things are just getting worse. I replaced the seagate drive with my original drive thinking that was the problem, it wasnt, ive reseated the ram (which was seated correctly anyway) i called apple, ran every test imaginable....aaaand, now i keep getting a black screen every time i close the lid and re-open it or if it goes to sleep and i try to wake it with my mouse or trackpad. if i boot up from cold i get a grey screen which turns into a circle with a line through it, i have to reboot at this point...i re-installed OS X six times as i was constantly getting error messages that my drives werent working properly and so re-installed OS X, the re-install worked for about a day..... then the same thing would happen, it wouldnt repair or verify and now it really only works 50% of the time...so you can imagine im massively disappointed.
I was thinking about paying out another 300 quid for apple care, but then ive only had it for under a month, and if you pay £1500 for something you expect it to work at least better than this....i read extensive info beforehand on additional memory and hard drives and both items were strongly comfirmed as compatible.

Given that my machine is under a month old i'd hope that Apple are gonna be at least a little sympathetic when it seems that they have sent me a duffer!!

Has anybody experienced anything similar? what was the outcome? any advice?

cheers all.

Umm if you had that many problems with it, why didn't you just send it back or go to the Apple store so they can take a look at it.

You are still under warranty which last for a year. Apple care is for things that happen after that one year.

Send it back and get a new one, you are still under warranty.

Hmm, it sounds like it's a problem with the Motherboard/CPU since it isn't the HDD or RAM. Things just don't seem to be computing properly on your Mac. I haven't heard of that many problems happen on a new Mac. You were probably just unfortunate and bought a defunct computer. Did you get it straight from Apple or a reseller? Your computer is under warrant for 90 days/ 1 year I think without AppleCare. You should just send it back to Apple and get a brand new computer.

Yeah, thats what i was thinking too. i got it straight from the apple uk website so its as fresh as they come and makes it all the more obvious that something is wrong internally, its kinda strange cause sometimes it works like a peach, but then just becomes really unstable and just collapses in on itself. I recently moved over from pc to mac for want of some platform and hardware stability so ive been pretty gutted, but its just bad luck i guess, every facet of the mac is vastly superior so i guess i'll just ride it out and get it sussed by the manufacturers.

cheers