with vista installed its been restarting or sometimes just freezing up
so a friend of mind tried to change some settings ( but i cannot find him now thats why im asking here)
and its been working fine for a week
he also advised me to changed OS to windows 7
so I did now I have windows 7 its been restarting or sometimes freezing and cant use ctrl alt del
i dont know what is causing the problem i want to know if its hardware or software or just some of my setting
I need help

sytem manufacturer: toshiba
model: satellite L300
BIOS: default system bios
processor: intel pentium dual cpu t2390 @ 1.86 ghz( 1 cpus) ~ 1.9ghz
memory: 2048 ram