PC Desktop 問題, PLS ＨＥＬＰ！ ， 描述： Ｍy computer is not working, hope you can give some comments

chongb

when i turn on my computer, it boots, and works fine,  it loads the windows too, but after a while (about 1 min)  the monitor will turn dark, and nothing shows on the monitor; however, the pc seems to be running still.    If i reboot it right away,  monitor stays black,  I have to shut down the computer for a while, then turn it on again, at this moment, it works, but after another min, monitor turns black again.     what's wrong with my computer?   i don't think it is my hard drive, i bought a new hard drive and try it, the problem is still there.  could it possibly be a video card failure? Thank you so much