Name1356

Okay so you're on the low end of the specs but, still possible for you to get things working. Your RAM is the biggest downside by the way but, let me see if I can help you.
 
I think perhaps your best option is to install a fresh copy of GTAIV. For everything to work, make sure you install it in it's default location. If you don't have enough space, clear some. It's vital so everything works properly. Test the game to make sure it works.
Once you get everything installed, patch it to 1.0.7.0 here: https://support.rockstargames.com/hc/en-us/articles/200145406--May-28-2010-Grand-Theft-Auto-IV-Patch-7-Title-Update-v-1-0-7-0-English-1-0-6-1-Russian-1-0-5-2-Japanese- Test the game again. Make sure it works.
After that, install LCPDFR here: 
Make sure you use the Automatic Install. When the configurator launches, configure it how you like. Test the game and make sure it works.
 
Install your mods and you should be good. 
If you need more of my help let me know!

Hello, I can try to help you. I need a few more details though.
 
What are the specifications of your computer? (Processor, RAM, Hard Drive(s), Graphics Card, etc)
Allow me to make you aware that making LCPDFR and GTAIV work won't be easy, but you can do it if you do it properly.