Radioshack mpa 250 amp

This unit looks to be a AC/DC PA amplifier. Here's an owners manual if you don't have one. That and a parts list is about all I could find. Mike
http://support.radioshack.com/support_audio/doc73/73142.pdf

The oil sensor may be bad, or the oil level may be too low. If the motor reads a low oil signal or no signal it will not start to protect itself.

Generally speaking, an amp attempts to protect itself from heat, shorts, overloads and operator exuberance by refusing to turn on or stay on.

Overloads can be from excessive periods of high output or marginally low impedance loading by the speakers; and shorts would be wiring issues or a speaker blowing up.

You should be able to feel if it's hot. WHY is it overheating? Make sure it has sufficient ventilation on all sides and that vent holes are not blocked by dust balls. Ensure the fan (if equipped) is running as designed (some only operate on demand). Clean dust and debris from it.

If the amp comes back on after cooling, you're lucky. They only have so many self-protection cycles in their lives so continuously resetting or cycling their power without addressing the cause can do more harm than good.

If it protects immediately on a cool power up you should disconnect the speaker connections and try it 'nekkid'. If it comes up then diagnose which lead(s) are shorted. If it does not come up the problem is internal and should be left to an experienced and competent hands-on tech.

Check for loose speaker connections at the speaker as another possible root cause for intermittent shutdown.

http://support.radioshack.com/support_audio/26947.htm

http://support.radioshack.com/support_audio/doc62/62610.pdf

for the past month i have been shopping for the perfect home theater system and have narrowed it down to a bose system,a sony system and a paramax p510...i have listened to all 3 systems and have found the paramax to be the better system not a cheaper system but seem more bang for my buck at 3200$,a very powerful tube amp and downfiring sub maxes out at 2000 watts...

Check the small electrolytics on the power supply board for high ESR, Very common problem on these amps. Protect circuit stays latched due to high ripple from PS.

ground, false power supply!

I can almost guarantee that you'll find bad electrolytic caps on the power supply board to be the cause of the problem. I've seen several of these with the same problem. The protect circuit stays latched due to excessive ripple.

As It was mentioned on the premium post, if after removing the fuse(s) from it, the amp powers up and stays ON; the failure is on the transistors or mosfets and they will need to be replace to get the amp working again on channel 4.
I would suggest to contact the manufacturers to get an authorized repair center to fix it under warranty if your amp is less then a year old.
Good Luck.