My daughter mistakenly put a stainless cookware inside and the microwave spark, now its broken

Check microswitches in the latch assembly.

Check splatter shield inside cooking area for burnt carbon ie replace

You probably fried the magnetron(it actually makes the microwaves that do the cooking). I bet you will find the magnet is broken(from excessive heat). There should be a diagnostic guide sheet somewhere inside the housing(due to running production changes,this is a guide for the pros to test the power supply,magnetron,etc with an ohmmeter to determine which is defective.

Got this from the "Answer bag" website:-

Cooks is the store brand name of appliances sold by JC Penny. The appliances are made for JC Penny in China by Sensio, an appliance company who also manufactures kitchen appliances for Chef Gordon Ramsey and the El Paso Mexican brand, among others.
Source:

Sensio

U.K. Telegraph: Gordon Ramsey Launches Cookware in Argos

International Housewares Association: Sensio Profile
More Information:

Fante's Kitchen Wares Shop: Links to Manufacturers

Consumer Reports: Cookware & Cutlery
Then clicked onto the Sensio website, couldn't find details or downloads for your over but on their contact page there's a phone number and an email address.
Customer service phone number: 1.866.832.4843 / [email protected]
Have a crack at one of those.

Stainless steel (or Aluminium) cookware will not normally work with an Induction cooker: Induction cooker need cookware that have a certain amount of metal especially at the bottom of the pot or pan.

An easy way to check if the cookware is suitable is to use a small (fridge) magnet: if it stick to the pot/pan then it is very likely that the pot/pan is suitable for induction 'magnetic' cooking!

Hope my small hint is of assistance and if so, vote accordigly!

There really shouldn't be a correlation between the metal ring in the oven cavity and the erratic operation of the control board. Although it might seem suspicious, what happens inside the oven cavity stays in the oven cavity.

Remove the plate and clean it with warm water

Yes you will not hurt anthing by not putting on the bottom. One substitution that works extremely well is to find you a plate like they use in regular ovens or anything that is microwavable of that sort. Sears has an excellent selection of microwavable cookware and there is nothing in the rule book that say you canno find you a piece to match the bottom of your microwave. It works either way. Good luck and God bless.