There are a number of remote desktop programs that should work for sharing a screen with Win7.
"Teamviewer" has long been a standard in this space, and is allegedly free for personal use ... but they have a reputation for annoying their free users by randomly accusing them of being commercial users and locking their accounts, even for relatively infrequent use.
"Anydesk" is another alternative. This is the program I still use for free when I need to provide support to my family, who live in different States. Though they seem to be trying to phase out the free tier, it's still listed on their "
Pricing" page.
"Distant Desktop" is yet another alternative, though their free use is time-limited monthly, so I don't know if that would be a factor for you.
The Achilles Heel with all of these is the traffic goes across the internet, so it's kind of silly if you're merely connecting two machines on the same LAN. Also, they're reliant on the companies' servers to make the connection between your two computers. AFAIK, your traffic doesn't actually go through their servers, but their server is required to transfer IP tokens to both machines and then the programs on your machines take over with a direct internet connection between them. But that paradigm leaves you at the mercy of the company, which can leave you high and dry if they decide to shut off their servers -- as happened with "Mikogo", another free remote screen sharing app that simply disappeared.
I believe the open-source "TightVNC" is supposedly designed primarily for screen sharing on the same LAN, but I haven't actually used it so can't comment further. If you can get it to work, that might be your best bet.
