Can someone please help?

[Apallo]

I'm a little surprised that no one mentioned this yet, but the rattling from the back of your computer might be coming from the power supply. There is a fan in it (sometimes 2) that help cool the supply and also help to draw air through the computer. If the PSU fan is going, you might have a potential fire hazard on your hands. I've had PSU's with bad fans literally explode on me (not as dangerous as it sounds, just unnerving when it happens) and have also had them catch fire (dust and heat can = fire). The rattling is usually caused by the bearing in the fan starting to give out, and when it does, the fan will seize. It can also be the fan that cools the processor, which if it goes, can take the processor with it. Try running the computer while the case is off, to see more precisely where the noise is coming from.