It may be that overheating is the main problem - I've noticed that the ol' pc does seem warmer in my lap than I remember from the halcyon days of its youth
Most 'laptops' are not intended to be used on the lap. (the name is very misleading). Laps tend to have plenty of give in them, and flesh which can block the outlets from the cooling fans.
If you must use it on your lap, use a tray, or a hardback book, which ensures a flow of air is available below & around the machine!