Windows 7 - self destruct ?!?

I've been using different OSes thru last 20 years but first time I don't know
what is happening with my computer .

Few days ago I decided that I want new Windows 7 . I've downloaded version
RC from torrent and I successfully installed on clean partition (I had another one
with all data files) .
But after sometime (few hours) strange thing is happening . No error nothing but
my disk is very much in use . I closed all applications , look in to task manager - nothing unusual .
CPU usage normal (few %) . After 15 minutes all my icons disappear . All software in start - lost .
Even software/icons in this new thing (i don't remember name - "quick lunch" ) is lost (icons are blank) .
I tired to restore system - but after few minutes system restarts and there is some error
that windows cannot load because he can't read some files (or files are missing ?) .

Ok I thought this is maybe some kind of nasty Virus . I've decided to do clean installation on clean partitions - I've deleted all partitions , formatted disks , downloaded latest version Windows 7 from MS (burned into DVD) , created new partitions during installation and .... the same thing happened after 30-45 minutes .

So far I've tried 3 times and all with the same result . Do anyone knows what the hell is going on ?
There is no error , nothing is showing up . Just unusual disk usage .
I have dell latitude 9400 laptop .

Please help

And as I mentioned before I thought that too ... so I decided to download directly from MS .
Clean installation , clean partition . formatted disk .
First installation was based on windows from torrent , second and third was on win7 from MS .