Slow Computer Solutions?

I'm pretty sure I have a "Toshiba Satellite" laptop, or something close to that model. Its about 2 or 3 years old and a few months ago it completely crashed and I had to get a whole new motherboard. I got it fixed at some cheep place at the mall, so that could be contributing to the problem. My mother claims that since the original motherboard crashed, then the laptop will never be the same, I don't completely agree, however. Bottom line is that since I got my laptop back it has been really sensitive and slow. Every time I take I it off the charger, bring into another room, and it moves to suddenly...it crashes. The internet is slow, word is slow, programs are slow...everything is slow! I took all of my unnecessary documents and programs off and I have a Norton protection system. I've ran clean ups and done everything I can think of but nothing is working. I have considered completely reseting it to factory settings but thats my last resort. Hope thats enough info. :) PLEASE help!!! Thanks