Cab files changing format

Sorry if i'm in wrong area but this is my very first post! My problem is when I download a .cab fiile or zipped file with cab in it when I try and install it the cab file changes from a cab icon to a windows icon and will not let me install. Some programs have been installes fine and some wont install no matter where i get the software and i'm getting frustrated. Im using a touch pro 2 pretty much barebones with just a few addons like reg editor. Please help
PS: Also when I open the cab file to install it says the file cannot be opened,either it is not signed with a trusted certificate or one of its components cannot be found, try reinstalling or restoring this file... Ive done this with diff files and still get same anooying message.
PSS: I just downloaded personalizer and mortscript from ppcg and it did same thing..also it dont matter if i dl from desktop or phone same result,i used to be able to install cabs with no problem..please help.