I'll say again, what are your computer specs? Are you literally running Windows XP? (Judging from your avatar, never know) Are you subscribed to a lot of Garry's Mod addons that conflicts with our content?
If this issue is only for the server perpheads, make sure you got all the latest content. Subscribe to the content here .
Also, if you could play normally before but after the new updates not anymore then make sure you delete the old content, and install the new content (This worked for me for the v4 update)
Also, verify your steam cache that could help aswell.