More questions! I keep hearing a strange noise every now and again from my computer, its a bit like a 'dong' kinda sound, it has happened alot today, I have no idea what it is, any one have any suggestions as to what it can be?

Thanks.

Don't know if this relates. But my Laptop will make a knock noise when the power adapter gets disconnected and it starts to run on battery.

Have you looked inside to make sure a wire is not being hit by a fan blade. While in there, make sure everything is clean and free of heat trapping dust. Be sure to discharge your body of static by touching the bare metal of the case before reaching in.

A failing hard drive can make mechanical noises too. I would make sure you have backed up any critical data you have. Also malware can do cause problems. I recommend you purge your system of clutter using Windows (XP or Vista) Disk Cleanup, ATF Cleaner or CCleaner. If you use CCleaner, then during installation, uncheck the option to install the Yahoo toolbar and before first use, go to Options > Settings > Advanced and ensure Only delete files in Windows Temp folders older than 48 hours is unchecked.

Note: Ensure you know your site credentials (user name and password) for sites you frequent before cleaning; you may have to login again at next visit.

Then download, install, update, and run Malwarebytes's Anti-Malware (MBAM) to ensure your system is free of malware. Then do the same for all other computers on your network (everything on your side of the Internet gateway, typically a cable/DSL modem).