I haved 250$. Is this cash enough for me to build a descent gaming pc? Or should I save more?

Solution
If you mean, from scratch, then no. $250 will get you a good graphics card, and thats about it. Here is a 'decent' gaming PC, which is around $680:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor ($174.88 @ OutletPC)
Motherboard: ASRock H97M PRO4 Micro ATX LGA1150 Motherboard ($70.99 @ SuperBiiz)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory ($46.99 @ Amazon)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($44.89 @ OutletPC)
Video Card: Gigabyte GeForce GTX 960 2GB Video Card ($244.98 @ B&H)
Case: Corsair 200R ATX Mid Tower Case ($47.99 @...

Mxhawthy

Distinguished
If you mean, from scratch, then no. $250 will get you a good graphics card, and thats about it. Here is a 'decent' gaming PC, which is around $680:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor ($174.88 @ OutletPC)
Motherboard: ASRock H97M PRO4 Micro ATX LGA1150 Motherboard ($70.99 @ SuperBiiz)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory ($46.99 @ Amazon)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($44.89 @ OutletPC)
Video Card: Gigabyte GeForce GTX 960 2GB Video Card ($244.98 @ B&H)
Case: Corsair 200R ATX Mid Tower Case ($47.99 @ Micro Center)
Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply ($47.98 @ Newegg)
Total: $678.70
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-11-23 11:11 EST-0500




This build is even cheaper, at $560 and this is pretty much the cheapest build you can get if you want to play new-ish games at decent fps and 1080p, although the CPU in this build will bottleneck slightly, unlike the first build:

PCPartPicker part list / Price breakdown by merchant

CPU: AMD FX-6300 3.5GHz 6-Core Processor ($89.99 @ Amazon)
Motherboard: Asus M5A97 R2.0 ATX AM3+ Motherboard ($92.99 @ SuperBiiz)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory ($46.99 @ Amazon)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($44.89 @ OutletPC)
Video Card: MSI Radeon R9 380 2GB Video Card ($188.98 @ Newegg)
Case: Corsair 200R ATX Mid Tower Case ($47.99 @ Micro Center)
Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply ($47.98 @ Newegg)
Total: $559.81
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-11-23 11:13 EST-0500
 
Solution
you could. however every part you buy would have too be used.
xeon x5677 50-60$
gtx 750ti 80$
dell t3500 mobo 50$
3 sticks of ddr3 2gig ram ~30$

you would then reuse your psu, case, and the hdd. you need above a 300 watt psu for this build.