Everything slows to a crawl over time
Vista
IE7
When I First log on all is ok.
If I remain logged on for an hour or so, EVERYTHING starts to slow down........programs slow to open and slow responses....... Right-click slooowww to respond, windows explorer sloooww to open.
Browser: links and tabs very slow to respond.
If I were to remain logged on and continue, browser and all would eventualy freeze

What is the make and model of the computer?

One possibility could be heat. One possible cause of that could be dust and dirt inside.

Is it old? Has it ever been cleaned?

Compaq Presario
A year and a half old.
It doesn't get hot.
never opened it up........yet--[to clean]