If you are using the VGA input on your monitor then you are best to use a VGA output on your video card.
A HDMI to VGA adapter would only make it worse.
Check that your PC is set to the correct native resolution for the monitor.
If the monitor does support a DVI or HDMI input, then a HDMI or DVI cable connected to the HDMI or DVI output of your graphics card would be better.