Thank you for your post.
Your tech service is correct. Adding a new computer to the network would not cause any problems to FileMaker Pro. It's purely coincidental.
Were your backups running properly before the new computer was added? Do you have an even earlier backup?
Please send me a copy of your damaged file and an earlier backup. I'll do my best to try and resolve it. With the product no longer supported, I'm not sure what else I can do here. I have sent you a private message (top of this page - right side - X Messages) with directions where to send the files.