Keep your old computer.  Use it for Quicken, Excel, and Word.  And back up all the data on it.   Get a new computer just for online use.

I have 3 computers sitting on my desk (OK actually it's a 10 foot counter mounted on the wall)  The oldest one is not online in any way.  I forget what operating system it runs, Windows newer than XP but without two digits.  It has a printer used only for it.

The middle computer is one I bought at a yard sale for a project that didn't happen.  It's kind of my DTN machine.  One tab is radar, another something else. 

My main computer is two years old.  It runs the latest operating system, has two monitors,  is incredibly quick, and the hard drive crapped out last week and I lost everything not backed up.

Back up ALL your information