Windows Crashes in Italy

I recently bought a new PC:

(P4 2800 HT on, Dual RAM 2x256, IC7G, XT9600 ViVo,
2xMaxtor Serial ATA 120G, network connection to optical
fiber)

and I installed myself WinXP Pro.

From time to time (more than normal for an average user)
the computer was automatically restarting. So I changed
the automatic restart of win after problems occour and the
blu screen appears with problems like:

STOP 0x0000001A (0x00000780, 0xC0307600, 0x81251A78,
0x85A12C28)

STOP 0X000000C5 (0X6CE10000, 0X00000002, 0X00000001,
0X80538105)

Please help me because I don't know how to proceed.

Cristiana