I have been playing GTA and it has been working fine for the last few days - until I installed a siren mod. After I installed it, I tried to run the game (as admin like I always do) and the starting screens worked for a couple of seconds, then it crashed. I tried deleting the siren and starting again, which went a couple of seconds further into the start screen, then it froze. I have done everything on the list of things to do that is shown before you start a topic many times before, so it cannot be that. I ran a diagnostic and it said this:

 

BEGIN *SIGNED* LCPD First Response Issue Report
Diagnostics Tool Version: 0.4.3
Operating system: Windows7 HomePremium (6.1.1.0 Build: 7601) Service Pack:Service Pack 1
System RAM (GB): 7.95
CPU cores: 4
NET Framework 4.0 installed: True
Visual C++ 2010 Redistributable installed: True
GTA IV - Installed: True
GTA IV - Install folder: C:Program Files (x86)Rockstar GamesGrand Theft Auto IV
GTA IV - Version:
GTA IV - Asi loader installed: False
GTA IV - Asi loader:
GTA IV - Asi loader valid: False
GTA IV - C++ ScriptHook installed: False
GTA IV - C++ ScriptHook valid: False
GTA IV - C++ ScriptHook version:
GTA IV - ScriptHookDotNet installed: False
GTA IV - ScriptHookDotNet valid: False
End of *SIGNED* LCPD First Response Issue Report
Digital signature: ijHNA9t2wvIy0248StbHMw==

 

I know that it says I should fix it myself, but I already have an ASI loader and scripthook! I checked the GTA folder and they were still there! I don't know why this has happened. The siren mod was the FedSig SmartSiren by Ofc.Chad. Help would be gratefully appreciated.
 

Run the LCPDFR installer as administrator, you are missing critical files. Also, download the latest patch found here: (http://support.rockstargames.com/entries/484496-Grand-Theft-Auto-IV-Patch-7-Title-Update-v-1-0-7-0-English-1-0-6-1-Russian-1-0-5-2-Japanese-). 

Run the LCPDFR installer as administrator, you are missing critical files. Also, download the latest patch found here: (http://support.rockstargames.com/entries/484496-Grand-Theft-Auto-IV-Patch-7-Title-Update-v-1-0-7-0-English-1-0-6-1-Russian-1-0-5-2-Japanese-).

I have already downloaded that, and I don't know if its still on or not (should be) but when I tried to install it again, if said 'Installation failed. Run setup to finish install' then it said 'GTAIV setup wizard ended prematurely', then it closed. What should I do?

Then your entire GTA IV is broken. Reinstall it. 

Then your entire GTA IV is broken. Reinstall it.

Does that mean I will have to reinstall all of the mods I've downloaded as well?

Well, yes, I would recommend that you remove GTA IV, and then manually remove the GTA IV folder. 

Then your entire GTA IV is broken. Reinstall it. 

Thanks for the help. I tried that then this happened: