|You need to find the reason for the crash, it could be hardware related, like faulty ram or hard drive. Asuming it's Vista at fault without checking, could result in a failure to install W7 if it turns out to be hardware.|
First try the restore to factory setting, you should have documentation telling how to do this, if not check the makers website.
There is no button to press to delete the OS.
You would need to format the drive using the OS boot disk.