r/QuickbooksOldVersion

I'm not a quickbooks expert but I have accounting experience. Please explain to me like I'm a new ie.

I started at a small family-owned business. Their old bookkeeper is mia. Turns out all of this year and some of last years data is missing. There are no backups it's just not there.

Where do I even start (April 2925 is the last check written and invoice).

Quick question: if I install QB 2018 on a new computer, does Intuit 'deactivate' the version on the old computer? I need to have both running for about a week while I build a new infrastructure. Please advise.