I am trying to add life to this computer so I can pass it on to a friends daughter. My question is , in the back of the case there is a plastic sleeve that goes almost to the cpu. There are no holes to install a fan and I don't understand the purpose of it. If the cpu fan is blowing air on the cpu it looks like it would be bringing air in from the back. Would it make any sense to pull the heatsink and reapply with artic silver since the cpu is older. The cpu seems to run at 100% a lot of the time so I want to cool the insides down. Any help on prolonging its life. Thank You

You can always re-apply thermal paste (it wouldn't hurt anything except maybe a few dollars from your wallet/purse), but I don't quite understand your other question. Can you post a picture of the "sleeve-like object"?

Will it help the cpu to apply artic silver?