Need help upgrading my old PC

Hey there!
I've got an old rig from 2007 that I’m looking to beef up a bit, and I could use some advice.
The motherboard is a Gigabyte GA-M57SLI-S4
The CPU is an Intel Core i7 processor
RAM is DDR2 2+1 400MHz
GPU is an ATI Radeon HD 5450 1GB DDR3
Mainly, I just use this thing for streaming movies and browsing the web, though I wouldn't mind playing the occasional older game on it now and then.
Any suggestions would be appreciated. 🙂

Check out what this guy wrote here

Basically, just ditch the power supply, the case, and the hard drive—keep everything else and just buy new parts to swap into your current setup.

You’d be able to run older games without much trouble, but honestly... trying to upgrade that old motherboard of yours isn't worth the headache. It's way too outdated, and you'd end up relying on used parts anyway, which is always a gamble...
If you don't mind spending a bit more, I'd skip that Pentium and go straight for an Intel Core i7 processor instead. At least it's actually useful.

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That motherboard is basically a relic from the Stone Age; there is absolutely no point in pouring money into it. If that board decides to kick the bucket, you are completely screwed. You’re much better off just grabbing an Intel Core i7 processor and an RX560, and you'll be more than fine.