My Mac mini seems to loose it's memory?! Please help,thanks!

[ruk110]

I have a Mac Mini and every time i switch it off and switch it off again it seems to revert back to some of its original states even after i set the dock up i set mail up and general settings across the thing, but then again not all of it changes. What could this be? im completely baffled. i dont have the original installation discs still otherwise i could have re booted the software and stuff please help Thank you

sorry forgot to say its a mac mini 1.5ghz intel core solo 1Gb RAM @ 667Mhz running Tiger 10.4.11