A laptop that sees moderate use should be cleaned every couple years if not yearly. If you are uncomfortable cleaning it yourself, take it to a local reputable computer repair shop or find a large chain which offers the service.

I say this as a prior service member and SysEng: Dell and HP are enterprise brands. Please stay away from them as an individual consumer.

Lenovo generally has good build quality and decent customer support. This all of course varies by region but they are certainly cheaper for the same performance (if not better).