How do I set up crossfire on my computer under $350?

You probably cannot setup crossfire on your current setup if you are asking how to do it.
First of all, you need to make sure you have PCI-Express slots on your motherboard. Then you need to make sure you have enough of the correct kind of connector pins on your PSU. You also need two compatible AMD Crossfire video cards (SLI if you are talking about NVidia). They also need to fit in your computer. If all of this works then you can continue reading.

You would buy two of these:
http://www.newegg.com/Product/Product.aspx?Item=N8...
(those were the best I could find for your budget.)
Then you would put them in your two PCIE slots and plug the connectors from your power supply into both. Turn on your computer and make sure it is using Crossfire in your AMD control panel.

MAKE SURE:
Your computer is big enough.
Your computer has two PCI-Express 2.0 Slots.
Your PSU is good enough.
Your PSU has enough connector pins of the correct type.
Your CPU is not going to bottleneck your performance (it's pointless to buy these cards then.)
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Hopefully things work out! :D

✔ Highest voted answer

Reply · Send thanks · posted 88 days ago · 1 person agrees

Basically what Tom said. Of course, if your PSU isn't of good quality and output capacity, you'll end up needing to take some of that $350 and put it towards a better PSU. Realistically, you're better off just buying a single, more powerful card. What do you own now?