The use of an ISO from another computer may not solve the problem, I would advice against it. All Windows are individual, with individual product numbers, it may be considered to be a try to hack or copy an existing OS = illegal. Not a good solution.
I would suggest to try to contact the retailer, to find the original installation, they may be able to fix it, they have the material to re-install. Or, contact Dell, how to get it fixed. Everything else is guess work, don't get in the jungle.