
Shure it is temperature dependent, but this does not clean all your
problems.
Based on some exp. I must say that the connections between the power supply
and the Monitor and Main Board are usable to this failure, Ram simms can be
badly connected due to some corrosion and the powersupply can be in the
last
phase (lower Voltage).

So you can do following if you are used to such technical terms.
1) Clean all mentioned contacts with contact spray
2) readjust the 5 Volt level of your powersupply
3) use a calm fan and think of preventing dust blowinÔ through the floppy!
   (a fixed piece of paper can prevent this)
if you don't know how to do it beg a friendly technician!

Christian Bauer