My 150 w spider III looses power after on for 60minutes. no volume, all preset button lites go off, but preset names stay lit up. Goes off for a few seconds, comes on, goes off. Have to turn amp off and wait awhile and start all over.

This is a tiny amp good for practice at low volume levels. You are likely overdriving it and the power amp chip goes into thermal protect. If you volume level is much louder than a small boom box, you are driving it too hard. Best to get a bigger amp.

TRY CHANGING THE KNOB SWITCH.

If cycling the power IMMEDIATELY restores operation, it is likely something in the DSP (Digital SIgnal Processor) area associated with the built in effects. Do a test... see if the signal using headphones drops as well...

This unit uses a TDA type of power amp and those can overheat and shut down... so also do a test running it a lower level to see if it fails there... If it doesn't, you probably are just driving it too hard... solution is to get a bigger amp to get more noise...

I am guessing that you are trying to replace the presets the amp comes with, with your own. In which case all you do is dial in the sound you want and then hold either the clean,crunch,metal, or insane buttons until you see the light flash. Usually hold it for about four seconds.

possible software problem

Manuals to all Line 6 products can be found on their website.
http://line6.com/data/l/0a06000f1627d4547c34accbca/application/pdf/Spider%20III%2075/120/150/HD150%20User%20Manual%20(Rev%20B)%20-%20English.pdf

After making sure your guitar cable is OK (they often cause the problem) check the inout jack on the amp. They often get broken by yanking cable sideways.

Sounds like your master volume is turned up too much. The channel volume will make the squealing go away(caused by high gain and humbuckers). The best thing to do is dial in your favorite presets and change the channel volume to the correct level with the master volume where you usually keep it. I use my Spider Valve at master volume at about noon and the channel volume between nine o'clock and noon. Let me know if this does not solve the problem......

Make sure both the master volume and channel volume is up. If that does not do it, take it to the nearest Line 6 repair center.
http://line6.com/support/serviceCenters/

there is an open connection, most likely right off the input jack ,causing this issue. Resolder it or retension the jack connection.