Good thing. The only Thermaltake power supplies I recommend these days are for the most only those which are in some way a part of one of the Toughpower branches, and even some of those are somewhat questionable because unlike in the past where all the Toughpower series models were very good, they've realized that people realize that and now have both very mediocre up to very good Toughpower models. And the very mediocre ones are likely just repurposing platforms that are merely derivative of some of their weaker lines but are using the Toughpower branding to avoid instant distaste by those who will still assume "Toughpower" branding means a good unit.
These days, without going into some of the less obvious options, I'd generally recommend sticking to something (And these models are VERY specific, so don't assume something from the same series but having a different identifier is a safe bet. G5 for example is NOT the same as G2, G3, G6 or G7 when it comes to EVGA Supernova units. Just as one example. RM is not exactly the same as RMx or RMi, although the RM models aren't terrible either.) from the Corsair TX, RMx (Or RMi, even RM in a pinch) or HX series, Seasonic Core series (Preferably one based on the Focus Plus platform) or Seasonic Prime series, EVGA G6 or G7 series, Cooler Master V series, Super Flower Leadex Gold, Platinum or Titanium series (Leadex III or higher), Thermaltake Toughpower GF1, GF2 or Grand series (Preferably Grand. There are a couple of different iterations of some of the GF models and they are not necessarily exactly the same platforms depending on the actual model number) or the Antec High current gamer gold models.
At 8 years old, your existing Toughpower unit (Whether it IS or IS NOT the current problem) is a ticking timebomb. That unit only ever had a five year warranty or less to begin with and at 8 years old even the best of power supplies is either past or approaching the point where it is even trustworthy anymore in terms of being a danger to any hardware you place any continued value upon.
In terms of the current system, does it still power on and run, but simply shuts down at some point? Regardless that you changed the paste, have you actually MONITORED the thermal status of the CPU (And you can't just use any regular monitoring software. The FX series units don't work that way. You MUST use AMD Overdrive or Core Temp and which both allow or require you to use "thermal margin" or "distance to TJmax" for monitoring of core temps since normal methods are not applicable to this architecture. In Core Temp you must make the settings change in the advanced options to enable "use distance to TJmax in temperature fields" for it to work correctly.
Given the also probable age of your existing liquid cooler, and the additional fact that with only a 120mm radiator it was never really capable enough that it should have been used with that CPU in the first place, there is every probability that you might be facing either a loss of the pump RPM signal, blockage resulting in a lessening or complete lack of cooling within the loop, permeation (Loss of coolant in the loop over time due to evaporation through the rubber lines) or an air bubble that isn't allowing the proper flow of coolant through the loop. All of which, or any of which, could absolutely result in thermal trip which would send the system into instant shut down.