Iomega HD turns off when IMac opens each morning

I added an Iomega HD to my IMac for Time machine. Works great except : I automatically have my computer turn off and night and restart each morning.
The iomega stays on overnight. (blue on light lit) However when the computer starts up in the morning the Iomega turns itself off (blue light goes out) I have to manually turn the power switch off and back on the Iomega.

Any ideas whether this can be sorted😕
Thanks

Any Ideas