So what's the total budget?
What kind of monitor will you be going for? You say "higher refresh rate": does that mean you'll be sticking with 1080p? That's definitely not what I'd recommend.
Here's about where I'd be looking for your needs...
Case
FRACTAL FOCUS 2 ARGB GAMING CASE (BLACK) Great little case
Processor (CPU)
AMD Ryzen 5 7600 Six Core CPU (4.0GHz-5.2GHz/38MB CACHE/AM5) Not top line, but enough for gaming especially at your kind of budget
Motherboard
ASUS® TUF GAMING...
Spend £1400 on a "meets the minimum spec" build and you can look forward to spending another £1400 in two or three years. Spend a little more and you get a really good experience now and a much longer lifespan and, ultimately, much better value for money.
That's a super monitor. You can get a lot for that money, though it's not a "no compromise" price!
Here's where I'd start...
Case
FRACTAL FOCUS 2 ARGB GAMING CASE (BLACK) Solid case
Processor (CPU)
AMD Ryzen 7 9700X Eight Core CPU (3.8GHz-5.5GHz/40MB CACHE/AM5) Current gen CPU. Not the...
You should spend way more of your budget on a monitor.
You might look at the Asus PG32UCDM, which admittedly costs nearly £1200, but is the best 4K monitor you can buy right now. Alternatively, there's the Alienware AW3225QF at around £800. It would be foolish to spend this much money on a PC...
If you have a 6900XT, I would keep hold of that for now. The 4080 would be an upgrade, but I doubt it's £800+ worth of upgrade. Then see what 5000 and AMD's equivalent might bring.
Also, if you already have a Windows licence and are retiring the old PC, you can transfer Windows and save £100ish.
Not the monitor I'd choose for a system of this budget, but not bad! But I would expect that monitor ultimately to be a bigger cost to your experience of gaming than most of the components in the PC... £500 or so would get you a much better one.
And a 4080 for 1440p is definitely overkill. This...
And it's not just the rated wattage (after all, AMD recommend a 700W supply for the 7700XT, so it should be sufficient even accounting for those peaks), it's also the quality. The CX supplies aren't ones I'd choose for a gaming PC. That said, it should be sufficient, which is why I'd be asking...
For all that your power supply and cooler are significantly less than I'd recommend, they really should not be causing your PC to blue screen or restart. I would advise you to contact PCS and ask for support. A problem with the power supply seems most likely, but it should not be happening and...
Depending on the number of ranks on the memory, JEDEC standard speeds for four sticks can indeed be 3600MHz.
Edit: Here's the spec from the AMD website:
https://www.amd.com/en/products/processors/desktops/ryzen/9000-series/amd-ryzen-7-9800x3d.html
You will probably not succeed in getting all four sticks to run at the rated speed. The memory controller just won't be able to handle it.
I would have strongly urged you to get a 2x32GB RAM kit, and indeed that's probably your best option now if you want to get it working at those speeds. The...
Yeah, it used to be easily possible, but since Windows 10 came out it's got a lot harder. Separate drives is the way to go now. (Though I admit I do it the lazy way and just run a VM, but admittedly I'm not gaming.)
I realise one thing I missed out above was the fact that I've omitted a Windows licence presuming you can transfer it from your old system. If you can't do that you'll have to pay for a new one, adding £100ish.
The CPU will not limit the graphics card in pretty much any modern game except the...
You can totally get a really good new PC for £2000, including a new monitor, and you can absolutely use old monitors as secondary, tertiary or even quaternary (!) displays, even if they aren't a close match in terms of resolution and refresh rate. Most graphics cards have four outputs (generally...