k43d

hey I'm having a problem where I tried to switch hard drives so I plugged the cords in and it worked but then i unplugged it to put it in the pc properly and now when i turn the pc on it turns on but there are more buzzing kinda sounds coming from the hard drive and it says no signal on my monitor and i have to hold down the on/off button for it to turn off if i press it once it doesnt turn off and i tried to switch back to the old hard drive and it did the same thing please help!