Gaming computer for 300$

Solution
You can barely build a PC for that cost let alone a good one.
Save up some more and get this at the very least.
Optionally, buy used.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Pentium G4560 3.5GHz Dual-Core Processor ($68.99 @ SuperBiiz)
Motherboard: Gigabyte - GA-B250-HD3 ATX LGA1151 Motherboard ($61.98 @ Newegg)
Memory: Patriot - Viper 4 8GB (1 x 8GB) DDR4-2400 Memory ($54.99 @ Newegg)
Storage: Western Digital - AV-GP 500GB 3.5" 5400RPM Internal Hard Drive ($24.95 @ Amazon)
Video Card: MSI - GeForce GTX 1050 2GB Video Card ($93.98 @ Newegg)
Case: Thermaltake - Versa N21 ATX Mid Tower Case ($24.99 @...
You can barely build a PC for that cost let alone a good one.
Save up some more and get this at the very least.
Optionally, buy used.

PCPartPicker part list / Price breakdown by merchant

CPU: Intel - Pentium G4560 3.5GHz Dual-Core Processor ($68.99 @ SuperBiiz)
Motherboard: Gigabyte - GA-B250-HD3 ATX LGA1151 Motherboard ($61.98 @ Newegg)
Memory: Patriot - Viper 4 8GB (1 x 8GB) DDR4-2400 Memory ($54.99 @ Newegg)
Storage: Western Digital - AV-GP 500GB 3.5" 5400RPM Internal Hard Drive ($24.95 @ Amazon)
Video Card: MSI - GeForce GTX 1050 2GB Video Card ($93.98 @ Newegg)
Case: Thermaltake - Versa N21 ATX Mid Tower Case ($24.99 @ Newegg)
Power Supply: Corsair - CXM 450W 80+ Bronze Certified Semi-Modular ATX Power Supply ($26.99 @ Newegg)
Total: $356.87
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-06-20 22:02 EDT-0400
 
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