Phew - the machine boots!

Had a bit of a scare this morning when the home machine refused to boot. Basically the computer froze after displaying the Bios version and CPU speed and refused to go any further. After taking everything out this evening it booted up so I then tried to remember what I had changed, and then remembered the (non powered) USB2 hub I got last week. Unplugged it and the machine booted up ok. Plugged it back in again, with nothing attached to the hub and the same thing happened. Therefore the hub is now sitting on my desk. Not sure whether I can be bothered going through the hassle of getting it replaced...the weird thing is that the hub works when the machine is booted up. Having said all that I'm wondering if the PSU is being maxed out as the machine also refuses to boot if I have a usb thumbdrive plugged into it when I boot up.