Did my USB 2.0 hard drive kill my laptop?

No. It didn't kill your machines. What it most likely did to your Desktop was nothing. Your laptop though most likely shorted out due to the eminence power needed to power up a USB HDD. Just let your machine sit for a while, then turn it back on. If that doesn't work pull out the battery and wait a minute and plug it back in. The worst that could happen is that the USB HDD has a virus. It can't kill your machines. Let me know how it goes.