Mass Effect on the PC was shipped with SecuROM. It limits the number of installations to 3.
I personally hit that limit because I have 2 PC's. I upgraded both of their Operating systems and had to re-install, which incremented me to a total of 4.
You can call, E-mail, or Live Chat EA about this issue and I was able to have them increase my install count after I described the process and issues I encountered.
