Offering a model number is always a better idea than a general category.
A blinking light sounds like a fairly major fault. Googling "onkyo blinking standby light" suggests the problem is, as dfergie offered, a short in the speaker system or cabling. The diagnostic procedure can be found in a number of the Google results.
After having speaker wire issues a couple times, I got some banana plugs to use instead. Much cleaner install and makes for easy switching out to a new unit going forward. And because of the way the decent ones are made, making a bad connection is nearly impossible.
Monoprice offers all-metal banana plugs in a 10 pack (5 color coded pairs) for $5.49. The pin version is $5.99.
If moving the receiver is dislodging the speaker cables, you probably need to use longer and/or larger gauge (smaller number) cables. 12ga copper (lamp cord) is good for up to 60' runs. Anything less than 16ga is questionable for all but short runs and relatively low power. I use 12ga for fronts/center and 16ga for surrounds.
Insulation can be missing at more than just the ends of the wire. Try disconnecting the wires altogether and see if it dies. Be especially wary of any wires that run near walls, furniture, under carpet or through holes.
If it survives without the wires hooked up, try adding them back until it fails and/or testing them with a meter. The resistance with the speaker connected should be more than 4 ohms.
You never know what kind of "help" that others in your home might be offering; others being humans (large or small) or animals (domestic or otherwise).
At that age it is usually the flyback transformer that starts going bad but I'd still go through the process of checking the continuity of all of your speaker wires. It is usually $100 to $150 for the replacement of it. If it is the power supply itself, that will cost a lot more. A shop will charge you $50 to $75 to look at it whether you have it fixed or not. Personally, I would just look into picking up a new receiver considering the age of the 505. Stick with Onkyo if you like the sound of your current receiver or go with Denon/Marantz if you want to stick with Audyssey room correction. Also make sure it is getting plenty of ventilation and check temperatures if you have a heat probe handy.