HDTV as Computer Monitor Problem?

Hi everybody, I'm having a problem with using my HDTV as my computer monitor, I tried to use this tv as a monitor before with my other computer and I had the same problem, basically what happens is when I hook it up to my computer using either VGA or HDMI the picture quality is really bad and all the text is really hard to read etc. I've tried different resolutions and refresh rates and played with the settings on my tv and I have had no such luck, hopefully some techie on here could help out. The TV I am trying to use is TOSHIBA RC-3910. my Gpu is Nvidia GTX 570 and on my other computer a GTS 250. Thanks.