Wow, sorry to hear that. What OS are you using? If you have WinXP, you don't need an ASPI layer, but sometimes it helps. If you didn't have it before, and Itunes worked, try using 'killASPI' from link below first.
If that fails to help, then you might want to try installing ASPI v4.60. You can get it from here
This will also remove the 4.71 version. There is a bit of an explanation there as well, just follow the instructions. They also have a little ASPI check tool that you can use. Your ASPI layer is also visible in Nero Infotool, near the bottom of the output file. You can install Infotool without Nero burning tools.
Somewhere you probably removed some file you needed for Itunes. You could try a system restore if you have it. As fritzi93 suggests, it is always a good idea to make a restore point before proceeding with any kind of program installation, just for this reason. But you never know when programs are going to fight . You could also try a WinXP system repair, instead of a full reinstall. If you have an HP desktop, that may have come with repair discs.
Once you get Itunes going again, maybe you can find a program that plays nice with Itunes from reading in the Itunes forum I linked before.
Keep on trying and let us know how it goes.