I found out that the motherboard was dead. The RAM slots weren't running properly (incorrect voltage).
Was that hardware damage?... If not sure, BIOS settings can be changed so voltage to RAM is more adequate, Even a BIOS reset can help if settings were wrong.
I've swapped most of the components into an even older 12 year old build! ( Now running Ubuntu 12.0.4 LTS as Xp's time is running out). Thanks for your help.
XP's end of support has already ran out, in some cases even since the last part of March... but that only means no new updates will be available from now on.. but all those up to April 7 will still be. And this doesn't necessarily mean Win XP will be much more vulnerable... I usually run XP SP3 in my old low resource computer with Automatic Upates turned off, for no other reason that Auto Updates is a constant boot lag... it takes minutes up to when System Idle Process goes up to 90's%... So, I rather update manually but, I forget to since I've had so few related problems that I plainly give it little importance. What I usually do is disable unecessary Services that are related to Remote access, Computer Browser, Server, Telnet, Telephony, I disable file and drive sharing, Remote Registry, etc. etc. I also use Avast Free antivirus which blocks malicious websites and downloads.. and I do some other stuff like regularly scanning with Malwarebytes antimalware, deleting Temp files, and unecessary junk with CCleaner and regularly delete temp files manually, watch what I install and how I install (custom install) since almost everything you install nowadays has other unecessary and malicious software ready to install with them. The worst infection problem I've had with XP was back in 2006-07 under SP2 'protection'. So, that scare rutine of XP support running out is mostly Microsoft's way of increaseing sales.. they have been doing it since Windows Vista came out and specially now that Windows 8 hasn't been so successfull.
If you know what to do to prevent infectons and hacks you can be safe, otherwese stick to Microsoft's advice, or use a Linux distro which in my opinion are a good temporary solution and better than Windows in a few ways but worse in others like the way they are structured, they're impractical for installing apps, their austere user interface, etc. There are also other software solutions for XP like Deep Freeze which restores the system to a good working state deleting everything from the saved state to present.. and there are other similar software (Clean Slate, Shadow Protect, Roolback Rx)... so using Ubuntu or any other Linux distro is not the only or best solution.