First things first, I’d but a new harddrive. You will want backups either way, it will give you space to run both Windows and Linux, but most importantly, sudden loud noises could mean your harddrive is about to crash, in which case you will lose everything anyway. If you’ve got an old spinning harddrive, upgrading to an SSD is going to make your PC faster even if you don’t move to Linux. Although for 10 year old hardware, I’d definitely prefer Linux over the increasing bloat of Windows. And while you’re getting the new ssd, also get a usb stick. They cost almost nothing. (SSDs, unfortunately, have gotten more expensive since last year.)