@dude
Yeah, I didn't test memory thoroughly, but the computer booted ok with just one stick in (and I tried both on their own). I'll do a memtest tomorrow, as well as replace the PSU just in case (with some crappy old one from work)
One thing I noticed is, from the moment I log into the OS, 38% of my memory is being used up - by two svchost processes. I have very little running, all I've installed is a codec pack, really. 99% of the time the HTPC is running windows media center. That said, nothing seems to go slow at all.
I don't think it's a bad burn - Installing Vista as a test had similar problems. I didn't try XP though, admittedly. I just wanted something with media center, and XP doesn't have it (and I'd prefer not use media portal).
As a last resort before I get a motherboard, I'll backup the files I have on there and try to reinstall Windows 7, perhaps with a fresh burn too. I remember I had a similar problem once a couple of PC generations ago, where inserting a CD would lockup the system - reformatting the computer fixed it.
Thanks for your help, guys! Getting a new mobo may be a good opportunity to get a HTPC case too, because I have an old dusty mid tower at the moment.
Regards
Rhys Andrews
UPDATE:
Tried a different PSU - still doesn't work.
Did the memory diagnostic test that windows 7 has - no errors.
I'm going to try one last thing: Installing an OS from an ISO with VirtualBox, and seeing whether it runs CDs from that. If it does, then I know it's a Windows 7 / Installation issue. If it doesn't, I know it's got to be the motherboard.
Thanks again for your help, guys
Rhys