I'm not an expert, but if the crashing continues even after restoring your backups, then I would assume that either something else is causing the crashes, or your GTA4 installation was somehow damaged.
Try removing ALL of your mods and see if the crashing stops. If so, add each mod again one by one until the crashing comes back to find the culprit.
If the crashing continues even with all mods removed, I guess you'll have to reinstall the game.
__________________ My humble GTA4 realism scripts:
Arrest Warrant — notoriety system with cop alert meters
Bank Account — store money at ATMs and earn interest
Deadly Wrecks — car wrecks hurt, seatbelt helps
Weapon Weight — weapons and ammo slow you down
Weapon Storage — store weapons & ammo in safehouses
Real Reload — more realistic reload model for guns
Hide Radar — hide the radar & health bars for HUD-free gameplay
Q6600 @ 3.0GHz || 4GB DDR3 1333 RAM || GeForce GTX 570 1.25GB
24" LCD @ 1920x1200 || Windows 7 Professional x64 || GTA4 v220.127.116.11