Could be the power supply. Plugging in the USB hub will draw more power, even if its only a little as your hub has its own power supply. If this is the case, the plug should stop booting even without the hub attached pretty soon as the power supply gets worse quickly once the capacitors have lost their electrolyte. NewIT sells replacement power supplies for around 10 bucks but shipping outside of Europe is expensive. Or you could hook up an external 5V power supply with around 10-15W.
A) Is there a wiring diagram etc which says solder A to B etc?
B) I have a number of such beasties (a large drawer full of wallwarts) & I am now (having done a quick look on the forum wrt "power supply problems") wondering whether the wall wart is the answer as they normally outlast the electronics they power (hence the large drawer full).
Which do people recommend the external wall wart or the replacement PSU?
For one thing is the PSU daughter board mounted ergo connect external psu & remove internal psu thus increasing airflow/cooling etc?
Could be something else, of course, but it seems the original power supply will always fail sooner or later.
BTW, I've seen this kind of failure on other devices as well. My NSLU2's power supply failed the same way after one year of uptime. Switching power supplies require special low-ESR capacitors with high temperature tolerance but for some reason it seems many manufacturers want to save the few cents those capacitors would cost extra...
Crikey I thought this died out in the late 90'es when pc mobo's had this problem wrt capacitors.....