Should I upgrade or buy a new computer?

I have a Desktop Windows PC 64 Bit.
AMD Athlong II x2 240 2.80 GHz
NVIDIA GeForce 6150SE nForce 430
4 GB Ram

I've never upgraded or put together a computer but I want a faster computer. I don't really use my computer for gaming, Only Minecraft. I also edit a lot of videos but it's slow for me. Should I try to upgrade and what should I upgrade to make my computer faster for editing?

Or should I just buy a new computer? I saw this one laptop for $750 that has 12 GB RAM, and a AMD A10 Processor. Should I get that one instead?

I would buy a new one.

The best bet is to build your own, there are many tutorials on YouTube and it'll save you a good chunk of money. If building isn't your thing, that $750 computer sound nice. However, I would still always get a desktop. It's more powerful.

We'd actually need a bit more information to advise you on that, such as the computer model, or the mainboard.

If you want to build a computer, it can seem daunting at first but it's not that bad. You just have to be aware that you're going to be the one doing all your own tech support and troubleshooting - yes, you can call the manufacturer of your video card, or motherboard, or whatnot, but you're the one that's got to do that. If you're fine with that, go build! It can be fun.

If you don't want to do that, remember part of what you buy when you buy a computer is their tech support and warranty - for some people that's a huge advantage over building.

That said, with the specs you've given, you're several generations back on video, and your motherboard likely won't support modern processors, so there aren't really any simple drop-in upgrades. You'd be building a new system from scratch.