some computer problems...

I am having problems with the hardware of my computer. I do not know the technical terms for many things, so please bear with me as I attempt to describe my problems. I have an eMachines M6805. Around 6 months ago or so I got a virus on my computer that was pretty messy. It took a while to get rid of it and I'm pretty sure that my current computer problems started at some point after the virus was finally defeated. These problems include... my laptop cannot switch from outlet to battery power without freezing (and vice versa). This means that if I pull out the plug while the computer is on I must manually shut down the computer and reboot it with the plug out. The same happens when I press the function key followed by any key on the keyboard with two functions. For example, F7 on my keyboard doubles as the brightness control. However, pressing Fn and F7 causes the computer to freeze. Also, when I shut down the computer (by going to Start, clicking shut down, etc.) the computer freeze at the "windows is shutting down screen" and I have to manually turn off the computer. My wireless is also a little unreliable, though I am not sure whether that is an issue with the model of my computer, the wireless network or the problems with my computer. If any one could lend some insight into my problems, how I might get them fixed, whether its worth it (im thinking of buying a new computer, since I'd like a lighter computer anyways...). Any help would be greatly appreciated.