Firstly, backup the "important" stuff - go to C:\Users and copy everything from there onto removable storage - a USB hard drive or similar.
Then, look at doing a full backup with something like the built-in backup software if you have that edition. You may want to look into a 3rd party utility if you don't have a qualifying version. Acronis make a good one.
Finally, if it's "acting strange" that doesn't mean it "could crash" and it sounds like fear, uncertainty and doubt to me. Backup anyway, and backup every week (at least) but generally Windows computers tend to "go that way" before long, and they get bogged down with errors etc. The only way to prevent it (and indeed, with all operating systems) is to keep a clean system and not to overload it with software you just don't need.