Hi. I have 2 PC, one with avast and one without antivirus.
In the first PC i can’t install a software(not antivirus, another software) but i can install it on the second.Why this?
Sorry for my English, thanks
Which is your operational system?
Which are the error messages when you try to install and fail?
No error message, the program doesn’t start. I think the antivurus block it at it installation!
My OS is WIN XP 1° edition
avast doesn’t block, it reports infected files so you would know (a very loud alarm and pop-up window) if it was avast that stpped you ‘during’ a program installation.
Your OS is well out of date which could leave you vulnerable to exploits that have already been patched by Microsoft.
What software have you tried to install?
It’ a Poker client, In another Pc it work, but not in PC with avast. I don’t know why!
Thanks
Welcome to the forums, Brando! 
A little more info on the Poker client could help someone give you more info on why this is happening.
Poker “Client” sounds like a piece of Spyware !?