|"how can ya say that it uses 64-bit DDR2 memory???"|
Because you didn't tell us it uses DDR3 until now. Regardless, the HD 5450 is a home theater card, not a gaming card. It only has 80 stream processors - ATI's low end gaming cards have 320 stream processors. You can argue all you want, but those of us who are familiar with modern video cards know that the HD 5450 is NOT good for gaming.
The following link is to a Sapphire HD 5450 w/1GB DDR3 memory, & guess what? It's 64-bit. To the best of my knowledge, there are no HD 5450s that use 128-bit memory - why would it be needed on a card with only 80 stream processors?
"even if i turn off the automatic restart feature the pc still reboots with a sound"
There you go. If the rebooting was caused by a software problem, disabling the automatic restart feature would cause the system to lock up & display a "blue screen of death". That means the problem is most likely hardware related. I don't know what "kKkkKKKKkkkkkk" is supposed to be? If it's a clicking noise then the system shuts down, the problem is probably an overloaded power supply.
"The Brand name for 300W PSU is liteon"
LOL. That unit sells for $7 online - YES, seven dollars! What does that tell you about it's quality? Why would you spend all that money on a CPU, board, RAM, etc, then connect it up to a $7 power supply??
LiteON 300W - $7
Since it was too much trouble for you to post the amperage specs, I'll do it for you:
+3.3V @ 18A, +5V @ 25A, +12V @ 19A.
You definitely need to upgrade the power supply. If that unit blows, it may take out the board & CPU along with it. Get a new one ASAP & make sure it's a good one!