from the support page. I followed this and I am playing now.
Aside from verifying your game cache and checking your connection with Steam, you may also need to manually run secondary installers required by this game.
If you're encountering issues with launching Far Cry 3, make sure everything installed smoothly.
Exit Steam entirely.
Browse to your Far Cry 3 installation folder (Usually C:\Program files\Steam\Steamapps\common\Far Cry 3\)
Run the following installers:
...\Steamapps\common\Far Cry 3\Support\DXSETUP\DXSETUP.exe
...\Steamapps\common\Far Cry 3\Support\VCRedist\VS_2010_vcredist_x86.exe
...\Steamapps\common\Far Cry 3\Support\VCRedist\VS_2008_vcredist_sp1_x86.exe
...\Steamapps\common\Far Cry 3\Support\dotNetFramework\dotNetFx35setup.exe
...\Steamapps\common\Far Cry 3\Support\GameLauncher\UplayInstaller.exe
...\Steamapps\common\Far Cry 3\Support\PunkBuster\pbsvc_fc3.exe
...\Steamapps\common\Far Cry 3\bin\FirewallInstall.exe
Reboot your computer and test any issues again.
OS Specific Troubleshooting
If the above does not resolve the issue and you are running Windows 7 or Windows Vista, please complete the instructions in our Windows 7 and Vista Troubleshooting FAQ.
If you are running in Windows XP, take the following steps:
Go to the Start menu, select Run, type regedit and click OK.
Navigate to the following registry key: HKEY_CURRENT_USER\SOFTWARE\VALVE
Right click and select Permissions
Check the Allow boxes for Admin and System for both Full control and Read.
p.s. uplay is the caca del toro