Operationally to use MB while surfing should not be a problem. However, isn't it a little counter productive to do so as we know that MB does not scan in real time? My thought is the potential is present to have a 'new" bug without warning or detection embed itself in an area of the H/D after it has already been scanned. The critter would not be detected until the next scan and thus in truth a user would not know for 100% certainty that the drive was clean. DA

yes Kathsgrdn always update malwarebytes or any program prior to running the full scan there usually will be new definitions to pick up and running in safe mode is a great idea many times the trojan or malware has processes running that prevent it from being cleaned and in safe mode much less is running. If you need more help just come on back and ask. Also a good idea is to reboot after those scans, many times in fact malwarebytes will say something about clean after reboot.

If you are doing an "image" or "clone" backup, that will include the OS as well as all your installed programs, updates, and document (pictures, music, etc.). Then if the hard drive is indeed failing, you can purchase a new one, not expensive at all now, install it, and use the clone to reinstall your entire computer with everything just as it is right now. There are several free programs that will make this type of backup for you if you can get one to install. This will save you a ton of work bringing everything up to date since XP has been around long enough that there are a ton of updates. I have used this one and find the GUI very easy to follow: Here is a link that might be useful: EASEUS ToDo Backup Free

Try running malwarebytes in safe mode with networking, get the mbam updates and run the scan in safe mode. You may have an infection that is causing that to happen. also check this post at the malwarebytes forum and you may want to follow the instructions that were given and create a post there for their assistance, always create your own post and get specific directions for your problem. Here is a link that might be useful: malwarebytes forum