Please run the first 3 free diagnostics listed here: Hardware Diags
They are bootable, so that will be easier than trying to do anything in Windows.
Please start with the bootable antivirus stuff, as that's what this description reminds me of.
You can install another copy of Windows 7 on another drive.
First, make sure you scan for viruses.
Then be careful that you don't overwrite anything that you want to save from the old installation.
I'm not familiar with the Inland Revenue stuff, but most programs have data files to store the data. So you can install another copy of the Inland Revenue program and then use the data file from the old program. I'd suggest posting for help in the General forums for assistance with the Inland Revenue program.