Laptop being bad

i recently bought an acer aspire 3050(i know it's s#!t but my other laptop was BSODing every 2 minutes)off a friend for NZD$100 (USD$65.5) he sold it to me as he had bought a new laptop and this acer was terrible (512mb RAM, 1.8Ghz sempron processor) it was loaded with vista home basic and boy was it slow!!(atleast 10 minute startup time). to fix this i partitioned the hdd and installed windows 7 rc, i also installed 2GB RAM. all was fine and dandy(startup under 2 mins) but for some reason the CPU is ALWAYS at 80%(50c idle 60c load) and above and keyboard response time was always 2seconds or more, shutdowns would also take about 5 mins and after it turned off for some reason it would restart(pain in the behind).

ok now heres the thing..
my mate called me up and asked if i wanted to go to a DotA lan party. i said yes. so i click on shutdown and packed it into the bag while it was doing so. i get to lan open the laptop and sure thing, it had restarted, except this time it was like a brand new laptop!(fast keyboard response, cpu at 10% on idle(35c)) i was like wow! what just happened? after we had finished playing DotA i shut it down and it only took 20 seconds without mysteriously restarting!

ok so now here i am at home writing this post using an on screen keyboard(mum is using the desktop) cpu usage is at 90%(55c) and wondering why it has reverted back to being slow.

could someone please explain to me what is going on with this laptop?

I play dota too even thought its off topic! you play garena 5v5 cw? anyway seems like your cpu doesnt like your house. Is there anything different you are doing at the lan then at home? different programs? I would try putting a new arctic silver on it and prob by a external fan to put under the laptop that will help cool it down. Your internet might be a difference slower at ur house then at his house! less stress on your comp !