Here's a link with a new MoBo, CPU, GPU, and RAM that would be a major upgrade to what you have (although, it's not the newest and best compared to whats out now). The price comes out to $367, but if you did some shopping around on these items, it could probably be lower.
This doesn't include an SSD like others have been talking about, and you'd need to make sure whatever you upgrade to will still fit within the restrictions of your power supply.
Don't just buy these based of what I think, let other people look at this too. I'm not a computer genius like hometeam, but I know a bit about building PCs.
http://pcpartpicker.com/list/2kVZ2R
PCPartPicker part list /
Price breakdown by merchant
CPU: AMD FX-6300 3.5GHz 6-Core Processor ($94.89 @ OutletPC)
Motherboard: MSI 970 GAMING ATX AM3+ Motherboard ($84.78 @ OutletPC)
Memory: Kingston HyperX Fury Black 8GB (2 x 4GB) DDR3-1600 Memory ($40.56 @ NCIX US)
Video Card: Gigabyte Radeon R7 370 2GB WINDFORCE 2X Video Card ($146.99 @ SuperBiiz)
Total: $367.22
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-10-28 12:12 EDT-0400