I was able to boot into an old live USB Linux drive (not sure how)
Sounds like an OS problem rather than a new hardware fault which is why booting from a different OS on your USB stick worked.
I couldn't log on to any of my drives.
still can't boot into the old drives
Could be a corrupt OS, a faulty hard drive or the newer drivers or kernel might not be compatible with your old hardware.
Some distros also have encryption enabled if it was encrypted you wouldn't be able to access your files by booting from a different OS drive either.
a brand new install of the latest Linux on a different hard drive from scratch still has the same graphics issues
Newer Linux kernels sometimes drop support for older hardware, so occasionally an older version can work better than the current release.
e.g I have Mint installed on a couple of old machines but I'm aware that the kernel with the latest release doesn't support the onboard intel graphics they have I think it also has problems with old NVIDIA cards.
So have you tried different distros / kernels since you started having problems?
e.g. Mint I would try 22.1 or earlier not the latest, they also have a debian version at the bottom of the download page:
Linux Mint is an elegant, easy to use, up to date and comfortable desktop operating system.
www.linuxmint.com
There are literally hundreds you could pick from:
News and feature lists of Linux and BSD distributions.
distrowatch.com
I know you have been using Linux for ages but do you have or can you download Windows 10 and use it just to see if the graphics card works under that OS; you don't have to activate it just run it long enough to see if the GPU works because you still don't know if you have got a hardware or software problem.
Have I understood correctly that is it the CPU that you suggested changing (the computer's processor)?
No I meant replace the whole computer but if you saw a graphics card for a few pounds then you could try that instead of your GTX460 before you replace everything.
I am very wary of setting init display first to on-chip because I tried disconnecting the graphics card completely but the monitors went on standby instantly, no signal at all and I don't want to be stuck on that setting without any way of accessing it again! Shouldn't it have automatically used the on-chip graphics regardless of the init display first setting if the card was removed? I'm not sure what the default setting is, but would the suggestion above of taking out the battery and replacing it allow me to get back in if I installed the card again?
Page 13 of the motherboard manual you posted tells you how to clear the bios: Remove the mains power cable, then remove the battery and wait for a few minutes.
There is also a clear CMOS jumper (page 16) but you shouldn't need to use it and if you do I strongly advise to disconnect from the mains and take the battery out first because shorting the jumper could damage something otherwise.
Page 18 tells you what the
(default) graphics settings are the problem is you are using a DVI cable and
the default is "D-SUB/HDMI" so you need a HDMI or standard VGA D-Sub cable if you reset the CMOS without a graphics card installed.
I think even for testing purposes, I would rather buy new parts, as second hand would only be an extra item to troubleshoot if it turns out not to be working!
It just depends what is available to you locally, most people would be happy to show you that something works if you can collect it.
No one is going to recommend buying a new motherboard, CPU and RAM then using it with a 15 year old hard drive and power supply, so if you don't want second hand parts then you probably need to build a complete new PC.
There are cheap ex business / refurbished PC's which are ok for basic use but some of the sellers aren't very honest e.g. installing Windows 11 on hardware that doesn't meet Microsoft requirements (Intel CPUs should be at least gen 8 for W11). That doesn't matter so much to you if you want to still run Linux but you need to be careful what you buy isn't a lemon and is a fair price for its age but we can't talk about prices or other suppliers on this forum.
If you want to build a new computer people will make suggestions on hardware if you post your budget and what you use it for but it might be better in a new thread, you also need to remember that the flickering etc could also be your monitors dying.
