Whats wrong with my LAPTOP!!!

Hey guys ill spell right this time ok.I have a year and a half old dell inspirion 15r from dell,the dell salesman on the phone insisted this laptop if i wanted to play games so i bought it, it came with a ATI Mobility Radeon HD 4650.So i installed a few games on it minecraft,stronghold 3, medal of honour 2010, sims 3,empire total war and some more games.It ran these games to perfection with no lag even empire total war online was not a problem.
So about 9 months ago laptop was on my lap charging away then it sliped down my lap hit my shoe and it broke to charger piece inside the laptop.So it was sent away and repared for free under warranty after some complaining to dell as they originally wanted 200 euro, but we all know how bad dell customer service is.Anyway it was fixed and shipped back to us.The whole computer was wiped as i expected so then i rein-stalled my games and some extra ones like counter strike source and team fortress 2.Just for later empire,stronghold 3 counterstrike and team fortress are are on steam everything else has a disc.
So after around 4 months while playing team fortress 2 on-line on steam it crashed the power went even when it was charging.I immediately turned it back on it cut out before I could select whether to start windows repair or start windows normally.So I let the laptop cool down and it started up fine windows repaired the problem but it never gave me a diagnostic of what happened, so anyway I continued.Then 2 weeks later playing counter strike source also on-line on steam it crashed, so I knew what to do let it cool down.It dawned on me then it must surely be the fan,but I continued.
Then while playing counter strike on-line on steam it crashed another time.So that was the final straw .I went to a computer repair guy he said the laptop wasn't able for to play games for too long and that i needed a cooler pad to help it cool.So handed him 20 euro for cooler he has a now fix no charge fee so no money wanted for time looked at computer.I went away a sad man no more long sessions of games.
I went home anyway and started the cooler it was grand started to play cod 4 pro mod not on steam and 10 minutes into game boom it crashed.I was mortified the game wasn't on steam how can this be I said.So tried with sims 3 same storey, mine craft same storey and medal of honour same story. Ok so it crashed today my fault I know but starting it back up after letting it cool it said your computer is not compatible with steam warning.So i was like wdf ?? So kinda stuck here at the moment don't know what to do any solutions remember theses points OK these are most important.
1. First got laptop ran games smoothly eg mine craft, empire total war and much more.
2.Broke sent it for repairs.
3.DELL wiped laptop during repairs.
4. I reinstalled every game and more like counter strike and team fortress 2.These 2 games are on steam.
5.Games start to crash while playing on-line.Eg. counter strike and team fortress 2.
6.These games are main culprits.
7.Sent to see what repair guys can do.
8.Says laptop isnt meant for gaming no laptops are.
9.Gives cooler to try help.
10.I go home play non-steam games cod 4 on-line.
11.Crashes try non steam games not on-line crashes crashes.
12.Today when laptop crashes says " warning your computer is not compatible with your computer"