RICO123 I don't know where you got PU.exe from we haven't used it in like 2 years. Please follow this guide to download plutonium.exe and set it up. https://forum.plutonium.pw/topic/531/how-to-install-plutonium-iw5-launcher
You should also download a newer copy of MW3, if you use the same version as tekno you are likely to crash and we won't help. You can get a newer copy for free by following this thread: https://forum.plutonium.pw/topic/448/how-to-download-the-iw5-base-game/
If you have problems afterwards, please make a new thread and do not hijack somebody else's thread.