Can I use my PC SMPS 12V 450 Watt for my Embedded System work
The PSU rating just means that up to 24 A is available to be drawn from the 12 V supply. Your board will draw what it needs from the 12 V rail, up to 1 A from what you've said.

However, that means that the PSU will supply up to 24 A into an overload or short circuit from your board or 12 V connections coming out of it. The PSU protection will kick in shortly (something like 10's ms) after the overload is detected and either limit the output current to 24 A or most likely put the PSU into 'hiccup' mode, which you'll find details of on the interweb. This burst/ongoing 300+ W of power is quite likely to burn out tracks on your PCB.

So, in short, if you use it, be very careful not to let your board short-circuit the 12 V supply, otherwise you are very likely to damage that board.