The word 'unusable' is correct and usable in written English.
You can use 'unusable' to describe something that cannot be used or put into service. For example, "The laptop is unusable because it won't turn on."
If there's no cancel option, artificially stopping the process may lead to corruption and an unusable computer.
Instead of pausing to produce a feast of handsome, arrow-shaped leaves, the plant races on up to maturity leaving only an unusable crop of creamish-green seed.
He has some claim to be the father of mathematical biology, but Stephen Jay Gould acutely described his book as an "unusable masterpiece".
The countertops, cooking surfaces and appliances were at an unusable or even dangerous height for a seated chef, and cupboards and shelves were largely unreachable.
Patients can neither skip questions nor give anything but fixed answers -- so no one can scribble in an unusable number like 3.5.
By giving it to the Soviets, American officials hoped, they would lead Moscow to waste time trying to develop an unusable nerve agent.
A "soft" kill switch only make a phone unusable to "an unauthorised user".
Another is a chance to use an otherwise unusable German word.
Missing values (and items with an "Unknown" response) can make an observation unusable, thereby reducing the sample size in any analysis or report.
Dominic Grieve defended it by saying it was a totally unusable law, a defence also used by the Irish government when it passed blasphemy legislation that I've never quite understood.
Although a tenant could break a lease if a "casualty" event rendered a building unusable, most downtown apartments did not suffer such extensive damage.
