Usb problem or Software?

I wasn't sure if this was a hardware or software problem. Ok, so I plug in my iPod 4th generation, and my mac g5 running os x 10.5 leopard freezes and a screen shows up saying I need to restart the computer. Ok so I do that and the screen comes up again. I unplug and restart and everything is fine. Now, I plug in an external usb HD and once again, the same screen. I unplug and restart. Now, I try a flash drive, and again, this screen pops up. I need help so I can use my flash drives again!
p.s. the screen is a transparent gray screen that slowly rolls down from the top of the computer and then it says your computer must be restarted please hold the power button.

 

mac help is solved!

thanks guys!