Hardware Issues

Hello forum. I could really use your assistance. I may be leaving tomorrow, so if you have more questions I may not be able to assist. Here is what I have so far, and PLEASE I need this help right now. My computer is in the crapper.
I have a Dell Latitude E5500 running Windows 7 (64x) illegitimate
At first I thought I had a virus and this is why. They symptoms are very slow speed after a while of running. If not plugged into a power source the screen starts to dim. I thought at first I had a virus that replanted itself stealing my RAM because whenever I reboot it goes away. Then my suspicions arose when it continued to get worse and after searching far and wide with no findings of a virus I thought it might be hardware related. So I went into system preformance and when I had checked before the RAM was at about 23% idling, and CPU 2%. What I hadn't noticed was the in the resource monitor it shows me that the CPU maximum frequency was pretty highand so was the disk highest active time (like at 100%).
This showed me that it may be hardware related. Is there something I am missing? Is it time to start investing in a new laptop?
Thanks

PS I have another issue which I'm not asking assistance for, but just informing. The plastic holding the screen together is starting to peel open on the bottom so that sometime it shorts out the backlight. All I have to do to fix this is close it and open it again and it turns back on. If that helps explain the dimming of the backlight, then good. But I don't think that is it because I don't have any regular problems with it