New PC stutters everywhere, what should I check first?

Start with temperatures, clock speeds, and utilization while the problem is happening. Check CPU and GPU temperatures, whether either is stuck at unusually low clocks, and whether one component is pinned at high usage when the system stutters. Also check that the memory is detected as 32 GB and running in the expected dual-channel configuration.

That can help separate a hardware or configuration problem from a software one before changing more settings.

Since Windows was reinstalled and the issue stayed, I would check the basics in BIOS and Device Manager. Confirm the BIOS sees the CPU, both memory modules, and the SSD correctly, and look for any device with a warning symbol in Device Manager. Check the SSD's reported health and whether it is nearly full, too.

If the BIOS is old, update it using the motherboard maker's instructions, then load default settings and test before turning on memory overclocking profiles or other tweaks.

Try a minimal setup rather than changing everything at once. Disconnect nonessential USB devices and extra drives, then test with one memory stick at a time in the motherboard's recommended slot. If that changes the symptoms, test the other stick and slots. A faulty module or connection can make a new system feel erratic.

I'd check Windows power settings and background activity, but don't assume that's the whole story. In Task Manager, sort by CPU, memory, and disk while loading a file or opening a browser. If disk activity is high and the drive is responding slowly, check its health and connections. If the problem appears across a fresh install, a repair shop is a reasonable next step, especially if you can bring the parts list and notes on what you've tested.

One thing worth checking is the display connection. Make sure the monitor is plugged into the RTX 5070, not the motherboard, and confirm the graphics card is firmly seated with its power connector fully attached. That may not explain slow file loading or shutdowns, but it is a quick check for poor gaming performance.