Once you know the version of Windows installed on your device, download the installers from the following links: You can also update Windows Defender definitions using Windows Power Shell.
Please read the entire post & the comments first, create a System Restore Point before making any changes to your system & be careful about any 3rd-party offers while installing freeware.
hl=+lost +access#entry3059425 Would anyone be able to assist me in this issue? Note: You need to run the version compatibale with your system.
If you are not sure which version applies to your system download both of them and try to run them.
I will also give links for downloading updates for Microsoft Security Essentials in the post..
First check whether you are using a 32-bit or 64-bit version of Windows 10/8.1/7.