if you have a floppy drive, the simplest thing would be to download memtest86+ from http://www.memtest.org/
The thing you'd want for using a floppy would be:
http://www.memtest.org/download/4.20/memtest86+-4.20.floppy.zip
unzip that into a suitable directory, there's a readme that explains what you have to do.
there's other versions of memtest86+ that use bootable CDs or memory sticks, but I don't know much about those.
Your friend might be able to help with those, if necessary
Perhaps due incompetence or oversight on my part, but I can't seem to find a version of this that can run from windows - I have no blank floppy's - or any other floppy disk at all, for that matter - as they are obsolete. Neither does my PC have a floppy drive, thus I'm screwed either way. I had hoped this software had a windows-viable version.
Wanoah, dust might well be the sinner here - as stated the PC is roughtly 3 years and have not ben opened for that entire duration. Translation; it has never been cleaned or de-dusted. I've known for quite some time that this needs doing but ya know, varranty etc. Also, while I did rule out overheating earlier - PC's heat-indicators never claim anything get's to hot, when I check - this might still be the case. Despite the dust caking up some palces all fans seem to run fine at least - and at maximum speed, from now on. (Up from medium.)
I'm considering if I should sent it in for service and just bite the proverbial sour apple - the bill, in this case - or say fuck it, open the cover, void the varranty and then just clean it out. The latter option might be the most reliable one at this point and this also allows me to remove and replace faulty hardware as well, IF that turns out to be needed. I'd like to know if any of my hardware is in need of replacement first though, no point replacing RAM or whatnot that's fully functional.
I've also considered for a while not upgrading to Windows 7 anyhow - and if it turns out parts need replacement I should order that along with a new windows OS DVD - after all I order my stuff from komplett.no, one of the msot reliable PC hardware retailers in the kingdom. Happen to be the one's I got this PC from too, and I'm told their rates for service is... steep.
Unless anyone else has any new advice or help to offer I'm going to fiddle my tumbs for a bit and consider my next move. I've a few options still and I don't really like any of them, fas as possible cost or predictable effect goes. Still, thanks all for the advice so far, it's been very helpful.