This usually means you haven't downloaded the servers content pack or you may be missing additional game content. Our servers only use CS:S content.
There are three ways to fix this, verify game files integrity, reconnect to the server, or download the content pack.
Hold C, goto drawing in the top left, and toggle the Shadows option.
Having bad internet can be defined by many different speeds but if you atleast hold a 25Mbps download speed it would download at 2.5 megabytes per second. Calculating this it would roughly take around 15 minutes to download our largest pack.