Gregerson, heres a problem I had with SA:MP. I could not launch it, the client did not work nor did the normal version.
Try making a NEW account on your computer, once you've done this you will find the launch file for GTA:IV in your program files. It may launch atfer this.
I had the same problem, waited almost 4 months to find a solution, eventually I found it myself.
Step by step:
- Make a new account on your computer.
- Log on to it.
- Go to your GTA IV directory in program files.
- Click on the launch icon for GTA IV.
It should then work... This is what I had to do with SA.

Good luck.