My motherboard model is DQ57TM,I wanted to connect my Tv with my pc but I realized that I dont have more DVI slots in my graphic card and I noticed that there is DVslot on my motherboard in the back of the computer. I connected the cable to it but it dont work, after searching what was that I learned that it have to be enabled to use GPU and Onboard gpu at the same time
Your board, as do most, disable the onboard graphics when you install an add-on card.
Also note that your board is from 2010, and discontinued/not supported.
If you want Windows 10, your board, processor, and onboard graphics are not supported.
It is unclear whether you can enable both the processor graphics engine and the add-in graphics card on a Desktop Board this old. Check whether this is supported in the Graphics Configuration scene in BIOS Setup. Al is correct, however, the processor graphics engine is not supported in Windows 10; you will not find a graphics driver. It is unclear whether the compatibility driver provided by Microsoft will support using both graphics engines.
BTW, if your add-in graphics card has multiple connectors and supports multiple monitors, there are dongles that will convert from other connector types to DVI. For example,
Using one of these will enable you to connect two monitors without the need to enable the processor graphics engine.
Hope this helps,