I've always kept the unit on the desk where I can easily access the CD drive, USB and SD ports.

I opened the side of the cabinet this morning and found the dust wasn't too bad. I used a combination of compressed air and vacuum for the dust, then alcohol to wipe and Q-tip the surfaces I could reach except the circuit board. There are three fans so I carefully cleaned all the blade s with Q-tips. I'm happy with the results.

I booted up but had previously scheduled a Windows memory diagnostic. No problem so far but it will be a few more hours until it completes. I should know tomorrow whether the cleaning had any effect. More then....