gmod model error? (HELP!)

i have been playing gmod for some time now and when my pc broke our family was given one by my dads friend it is about 4 years older then half-life 2 and when ever i play any source game it always has a error like this


but whenever i play any mod which uses the source engine it is perfectly fine (NMRIH,zombie panic source, ect…)

does anyone who is reading this post know what is and happening and could anyone give me a solution. use this link if the image is broken