If you want any meaningful advises you'll need to at least properly describe your setup. After all this time you haven't even said what GPUs you run.
There's plenty of reasons for any computer to reboot by itself, and even more so for a mining rig. Both hardware and software reasons. Unless it's something very obvious, it's unlikely that someone will figure out what's going on with your rig simply because you didn't bother to spend a few minutes and actually describe it. Cards, risers, PSUs, how exactly it's all connected together etc. All we know is that it's tb250btc and you're using 1000w and 500w PSUs one of which is an old Antec. That's like a riddle, you posted only a few clues and then you wait till someone will solve it by guessing everything else. Except obviously no one here cares whether your rig will keep rebooting or not.
You're the only party interested in solving this, yet you don't even want to bother with providing all the details.
The usual suspects in problems like this are the risers, the power (both how it is supplied and with what PSUs), the GPUs themselves and the system (motherboard/cpu/ram). You start by swapping the risers. If it doesn't help then you check the power, install another PSU, check whether all the connections are alright (so there's no nonsense like 3 risers sitting on a single cable from the PSU etc). Didn't help? Change the board. If it doesn't help either then test all the GPUs one by one. That's how it's done in general, it's just with more experience you're more likely to find the culprit faster, but the process remains more or less the same.
