no signal sometimes, but pc boot fine

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My computer is working fine , and during its operation is no problem , but when switched on, about three out of five cases , my monitor shows " no signal " . Thus the computer is always loaded and running ( audible sounds enter the system. l When the monitor show me NO SIGNAL i have tryed to connect pc at tv with HDMI and have not see nothing. When the pc running ok if i connect pc at tv i see desktop on my tv. So, i think that the problem maybe is graphics card..... I HAVE GTX 670 palit, and gigabyte UD3h z77 intel i5 3750.

I forget that when the monitor show mw "no signal" the pc and windows run fine because i listen audio boot. And if i shut down pc from keyboard the pc shut down regolary.

Please help.

Thanks!

I didn't find the right solution from the Internet.

References forums.geforce.com/default/topic/741836/no-signal-sometimes-but-pc-boot-fine/

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