Install problems

[Gafgo]

Hello there! I am a newbie to FreeBSD but have read a lot of handbooks. 
I have also installed different versions on my old computer just to 
practice (incl 4.8, 4.9, 5.0, 5.1). Now I have bought a new computer and 
wanted to install 4.9 for real. But during boot up this happened:
ad0: REAL command timeout tag=0 serv=0 - resetting
ata0: resetting devices...
and there it hangs. When I tried 5.1 I had no problem. Could it be a 
hardware problem??
I hope that somebody can help me with this.
Many thanks Nicolas