Lol, you made a terrible mistake, bring GTA IV back already.
Now, 2 things:
1. Your pc is probably to outdated for GTA IV, could you post your PC specs? 1 GB and 7300GT are under the minimum requirements, so you cant run the game at all. I think your processor is a Pentium 4 or something, according to your GPU and memory. You have to buy a new video card (''GPU'') and some new memory (''RAM''), and probably also a new processor. And now, i advise you, dont buy the parts that you need to just run GTA IV, buy a complete new computer. Not from the store, but buy the parts by yourself (i or somebody else on the forum could help) and let someone make a computer out of it.
2. Maybe you melted your video cart by running GTA IV. GTA IV is way to heavy for your card, and that could overheat it easily (if you dont have a good cooler). Im not sure about this though, but i think thats the reason why you cant start any game.