Thank u for your suggestions guys, but i have tried another power supply (more powerful than the existing one that i have) and still it doesn't work. I don't know much about BIOS, i wanted to upgrade it but i'm afraid that its causes damage to my mainboard. The video card works on other mainboard but why not mine? i have gone to see a technician to solve the problem, he says that my PCI-E slot isn't recognizing my card. I have even contacted Biostar, it says that 'P4M900-M4 motherboard supports PCI-express 16x 1.0 video cards only (first generation). PCI-express 2.0 video card is not compatible.' How can i know if my PCI-E x16 is disabled or enabled? What should i do?