I have a windows 7 computer that has run fine for a couple of years. I was away for a month and left my computer off and after I returned, it worked fine for a few days and then I got a series of blue screen crashes. Then it failed to even turn on. You can see a power led lit on the motherboard before it is turned on but when I turn it on it won't show anything on the monitor, it makes no beeping sounds at all, and after a little while, it seems to restart itself and try again but I get nothing at all on the monitor and it won't go into the bios setup or anything. I took it apart, cleaned everything and reseated the ram and all connections, but it refuses to turn on or show anything on the monitor. I tried putting the ram in one stick at a time and in different slots, but it made no difference. I hooked up the hard drives to another computer but they seem fine and I can read and copy stuff. Can anyone please advise on which components may be causing this? The motherboard? The ram? The cpu? The graphics card? The psu? Something else? I do not have a second computer to try swapping components around to see which work. Thanks for any advice.