Either something is wrong with the reg file or make.exe is not in PATH.
The latter is somewhat easy to know.
Double click on sh.exe in c:\PS3SDKv2\MinGW\msys\1.0\bin. The console will open & you can run make -?
If you get command not found, it means sh cannot find make.exe
You can also run echo $PATH to display the list of paths the system scans.
There are 2 ways to add a folder to the PATH environnement variable. You can add it permanently or per session using the command line, cygwin/mingw/msys configuration files for bash or profile or a batch file.
The latter is what you usually get in ps3 projects building batch files.
If you wish to add a path permanently, right click the My Computer icon, click Properties then Advanced System Settings & System Properties window opens up.
Click on Environment Variables & in the System Variables section, edit the "Path" entry. Just add the path with a semi colon at the end at the beginning of the line.
Like so:
C:\PS3SDKv2\MinGW\msys\bin;...
If you have several installations of cygwin/mingw & msys on your system, you may also face situations where an executable is found but it belongs to the wrong installation. For instance, make.exe is found in cygwin/bin because that path is first in PATH & sh.exe in msys will try to use it, usage may succeed, fail or be in between ie some things work OK but others don't.