Setup freezes at "Expanding Windows files" and a little more...

I wanted to install Windows 7 x64 Ultimate onto my brand new computer and the installer freezes every time at the "Expanding Windows files" screen, not always at the same time, e.g sometimes at 44%, sometimes at only 80%, or it also happened that the machine rebooted in the middle of the process without prompting or anything. Since I was unable to install the x64 version, I tried to install the x86 version, or e.g. Professional instead of Ultimate, with no success, because it also freezes the same way. I also tried installing from a different DVD, even from a pendrive, but this doesn't solve the issue, the setup just freezes at the same point. Unfortunately I'm also unable to install Vista instead of Win7, because the problem still persists. It seems that none of the above systems work...

To be able to use that computer at all I wanted to install XP then, but I also have issues with XP, because the machine also reboots sometimes without prompting, it also rebooted at the end of the installation process without any reason(when finalizing settings, such as users, automatic update, etc.) On XP, I'm also unable to install the graphics card drivers (ATi HD 5770), because after installing the Catalyst software suite, there is no picture at all after rebooting, after loading the system, the screen simply goes black, then the only thing I can do is to start up in safe mode, and to remove the driver.

Since I also encounter problems with XP it's likely that there's some hardware problem...if this is possible, then what can I do, or what might be the reason? Thanks in advance.

@theog: As I described above, this is a new computer, which actually differs from that, to which my system specs are referring.

Anyway, I will try to install Win7 with removing all non-necessary devices, incl. any USB devices. I'm planning to clean the HDD then as you described. We'll see if it works or not.

Thanks for all your responses, but removing the USB devices didn't solve my problem, I also unplugged the USB mouse,(used a PS2 keyboard) and erased the hard drive completely, but the installer exited with an error message approx. at the half of the installation process.

Since that computer has valid warranty yet,(because it's actually brand new) I'm not able to remove memory sticks without losing the warranty, so we contacted the manufacturer of the machine to work around this problem. They're currently testing the machine in order to find out what the problem was.

Anyway thanks for your help, we'll see if it'll work correctly.

Today we got the results, and it came to light, that the CPU has an error which prevents the operating systems mentioned from working properly. It'll be replaced for tomorrow, and let's hope that there won't be any problems in top of that!

Anyway, thanks for all your help! :)