Normally in a PC this type of issue is likely RAM, either just bad contact, a failed module or failed slot.
For bad contact, try swapping the memory modules (since you probably have two). If that still fails, put in the RAM again more tightly this time. If we have luck, the computer should boot with both memory. But don’t get excited too quickly, because while it detects the memory fine it could still be unstable and hangs when installing/loading/using Windows. We should test it for stability with a diagnostic/stress-testing software like memtest86+.
To test for a failed slot, you may try putting the working memory into the other slot. Check for errors. If it works that way, it is most likely the other memory has failed. To confirm that, test by plugging in the memory into slot 1 first and try booting up the computer. If it fails, try again with slot 2. Again, check for errors if it detects the RAM.
I also encountered a weird problem about RAM with my TR1 a while ago. The machine would hang / would not boot up for reasons unknown. And the cure was to put a small sheet of paper between the RAM and the casing to separate the two. It all went smoothly since then.
