Why is my computer screen black?

Please help to fix my computer screen turn black after running for like 20 minutes.?

• Problem: when i turn the computer on it run fine till 20 - 25 minutes the screen turn black. I have checked my graphic card and ram by replace the other one with same model ... but it still does not work for me. The problem happen again and again. This computer is my first self build. I bought all the parts from neweggs.com And here are my comp config: -HITACHI 0A38016 1TB 7200 RPM 16MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive -AMD Phenom II X4 945 Deneb 3.0GHz 4 x 512KB L2 Cache 6MB L3 Cache Socket AM3 125W Quad-Core Processor HDX945FBGIBOX -GIGABYTE GA-MA790XT-UD4P AM3 DDR3 AMD 790X ATX AMD Motherboard -AMD Phenom II X4 945 Deneb 3.0GHz 4 x 512KB L2 Cache 6MB L3 Cache Socket AM3 125W Quad-Core Processor HDX945FBGIBOX -SAMSUNG Black 22X DVD+R 8X DVD+RW 16X DVD-ROM 48X CD-ROM 2MB Cache SATA DVD Burner - OEM -G.SKILL 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Dual Channel Kit Desktop Memory Model F3-12800CL9D-4GBNQ -BFG Tech BFGE981024GTOCE GeForce 9800 GT OC 1GB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card -NZXT Performance Power PP800 800W ATX 12V 2.2V SLI Ready CrossFire Ready Power Supply -Sunbeam Transformer IC-TR-US-BA-WOPSU Black Steel ATX Full Tower Computer Case Please help me! PS: After i finished put all the parts together and turn the computer on it worked fine for like 5 months and then the screen turn black after 20- 25 minutes run.

• Answer:

  It may not be the computer, but the monitor itself. If this is an LCD monitor, then there's a real possibility that the backlight or the inverter is failing after that amount of time. Try simply turning off the monitor for a few minutes then back on to see if that brings the screen back instead of powering the whole computer down and back up. If that works, then you have a monitor problem. The other option would be to try another known working monitor on your computer or your monitor on another computer and see what happens.