Without a backup, it could be difficult/risky to try and do any disk maintenance/repairs. As it is, your machine is 10 years old, and if it still has the original hard drive, that could cause issues.
The first thing you should tryis to use another browser, and see if the issue remains. Also, you need to start making backups to an external device.
By the way, what exactly have you done regarding disk cleanup/maintenance/repairs? And how often do you do that? Finally, when was the last time you did it?