Am using Windows 07
You might consider switching to windows 10.
Windows 7 is outdated and - by far - less secure than windows 10.
Electrum 4.0.0
From electrum.org
As others already mentioned, there is no electrum 4.x.
It seems like you have downloaded a fake wallet.
Unfortunately there is no way for you to get your coins back.
But do NOT send any coins to any address whose private key is stored on your computer.
To be safe, backup your important files, format your hard drive and reinstall windows (preferably windows 10).
This is the only way to be
almost completely sure your computer will be clean (Exceptions exist: Rootkits for example, even tho i don't believe those wallet scammers even know what this is, let alone how to create one).
I believe I verified the signature
You 'believe' ?
If you didn't download ThomasV's public key and verified it with the signature file, you didn't.
And if you did, you would remember.
I worked with the default seed
There is no 'default seed'.
Each seed is individually created. This might be another hint that you have a malicious (non-original) electrum version installed.
I shared once with a relative
I have saved it on my computer
Never share your seed with anyone. Everyone with access to your seed has access to your coins.
Also.. never store the seed on your computer. It creates a lot of risks and ways to steal your coins. Only save it offline (preferably on a non-digital device) or inside of a hardware wallet.
Especially for not that techy user, a hardware wallet is the best option to securely store coins.