Try Malware Bytes and TDSS Killer (running TDSS Killer with TDSS file system checked off). If not, open up an Elevated Command prompt and type chkdsk /f.
If that doesn’t work and you have the excel disks, just uninstall and reinstall Excel.
It could just as easily be a virus as it is application corruption on an older machine.
Best course of action - get a Mac or an iPad and you can skip all the anti-virus cost and have a much more enjoyable experience. You are using a non-supported operating system that is prone to exactly the type of issues you are experiencing. If you enjoy the pain, keep patching it and restoring and wiping the hard drive and doing safe mode and asks strangers for help.