I have a dual screen pc display problem that I'm having trouble diagnosing. I have an October 2009 store-bought, out-of-the-box Compaq pc [AMD Athlon IIx4 620 Processor 2.6 GHz || 4 GB RAM || 64-bit OS] with 200GB free on a 500GB hdd.

I've had dual monitors about 18 months with zero problems prior to a month ago : an old Dell 17" that is fine and a Samsung 23" [model LS20AQ....] that has been "playing up" in this last month.

I've never noticed any hdd problems but the tower sits on (a cardboard sheet) on the floor of very old, dying carpet. I vacuum regularly, am careful to do the spaghetti and the pc and its intakes/fans and open the box about 3 times a year and carefully clean. The disc drive has made no weird noises, beyond the odd fan speed change that's not really anything I'm sure, and I don't think I've had any other problems at all with the software or hardware since purchase.

Just by the by, I've had a 1TB ext drive hooked up for about the same amount of time that the screen has been playing up. I don't see a connection between the two : it feels like a coincidence and I may even be wrong on the dates. Note: it's not an actual backup drive with its own software; it's just storage and I backup once a week using the Win7 software in Control Panel.

OK.... there are 2 plug holes for monitors on the back of the pc necessitating that the Dell connects to the tower via an adaptor (no biggy). The Samsung connects to the pc directly via the regular ummmm.. whatever it is... 16pin plug or whateveryoucallit. The screens have always worked this way without problem before last month.

What happens is this... (& this is only approx description in a lot of ways. I didn't take a lot of notice to begin with; I was just trying restarts etc really fast just to get the bloody thing on so I can't vouch for certain as to all the ways the problem has manifest itself)..

I start the pc and turn on the main Samsung monitor and .... nada. There appears to be no signal reaching it (the intermittent blinking of the power light continues unchanged; whereas it stays continuously blue when a signal is received).
If I turn on the Dell monitor, sometimes (often?) the startup screen appears and I can put in the password and it will boot properly but at other times that screen also remains blank. Sometimes all the main screen folders end up on the Dell and the main screen (in Screen Resolution) has been changed without my help from the Samsung to the Dell.

I have often just turned the machines off at the wall if I can't access a restart link from the Dell monitor and basically keep rebooting (often 4, 5, 6 times and getting longer now) until the screen appears in the main Samsung monitor. Occasionally the screen appears ok in the Dell and then automagically appears a couple of minutes later in the Samsung. In other words, there are erratic profiles of symptoms that appear in a kind of random way; or, at least, as random when there's a finite number of screens and manifestations of problems.

I have just now (finally : it's been a weird problem and I'm bloody lazy!) swapped out the Samsung monitor for a ViewSonic monitor of about 21" and approximately the same thing happened during booting : nothing on the ViewSonic for the first few boots, the main screen changed to the Dell and all the regular desktop folders moved over to the Dell.

So it would seem (to me) it's not the hardware.

Please note that I am what you might call "fair" in terms of being technologically capable or proficient. Don't be thinking that I have tooooooo much knowledge though.

I don't believe I've added any or much new software in the recent past. I have MS Security Essentials running all the time and I'm fairly careful about what torrents I d/load. CCleaner runs on startup; I also run SuperAntisypware from time to time.

In case it wasn't clear, the dual screens are maintained via "screen resolution" from R-clicking on desktop. In that window I choose landscape display and "Extend these displays" and use the recommended resolutions for each screen's display attributes.

So yeah... does anyone have any idea how I might go about diagnosing this problem and, if we just accept that I can follow orders but probably not toooo much else if it gets esoteric, what I might do to rectify it ?????

Please let me know if I haven't supplied all the relevant info. I can't think of anything else program-wise that seems relevant from the last month at any rate. [if you want details on the graphics card, please tell me how to find them]

Cheers.