According to the Owner's manual, P114,
If the unit enters Standby immediately on switch-on then it could be the unit entering Protection.
What I would do is disconnect all the loudspeakers and inputs and then switch the unit on. If it still doesn't stay on, then the fault will be internal, possibly in one of the power amplifiers, or possibly the control microprocessor. At that point you'll have to take it to a Service tech who knows the product.
If it does stay on, then switch off and connect the loudspeakers, making very sure you don't have any stray wires to short out. Try switching on again.
When you say you were given it, do you know if it worked before you got it, or is that why you were given it?
Sadly, products like these are generally reliable, but when they do go wrong, are often beyond economic repair if you have to pay for a Service tech.
Good Luck.
S.
