Alienware X51 Continuous beeping no boot, freezes, blue screens and random shutdowns

Hello!

I have a 2 year old alienware X51 that has, for a long time now given me much trouble.

When it boots, it will randomly freeze (Have to forcefully turn it of via the power button), blue screen or reboot. This mostly happens with applications such as Chrome or even Windows Explorer, it rarely happens when Im playing videogames or doing demanding tasks. After it reboots, it just won´t turn on. The screen stays black and it keeps making a beeping noise indefinitely (the most i counted before turning it off forcefully was 23). After this, I have to wait a couple of minutes and try again. Sometimes, the same thing will happen, others the computes will work fine (playing, browsing the web, etc) until I turn it off normally. The strange thing is this behaviour sometimes occurs for 1 complete week or many weeks, then It won´t have trouble for some days, weeks or even a couple of months (rarely). I already took it to my local Dell Store where they checked it and only told me that they had to do a complete formatting (which I have done myself on numerous ocations).

At first, because of the screen freezing I tought it was the video card, so I changed it(I also wanted to upgrade it) from the gtx 550 (the videocard it had from factory) to a GTX 660 (Yes, I know it is not supposed to be upgraded to a 660 because of the PSU but I upgraded and have been playing with it many high end games with no problem at all, also to notice that the problem started with the GTX 550 so the GTC 660 has nothing to do with it).

Any help would be very much appreciated since it seems that Dell Store couldnt suggest anything better than formatting...