Overheating

When I'm doing anything CPU intensive and I have my laptop on a surface (not on my fan cooler) it switches itself off because it gets too hot.. Now when i was repairing i took off the heat dissipating sticker that was bridging the cd drive and the cpu... that seemed to have made it worse so was wondering if anyone could tell me where i could get a similar sticker? and also how can i help this overheating issue, thermal paste? (but where?).

P.s. overheating issue did not happen before i took the sticker off but obviously it seemed to have been made worse after