Problem when restarting my PC

Hi my friends. I am here with problem, which i need to solve , and it is very important.

I have an PC.

2GB DDR2 RAM
AMD Semphron 2GHz
And i use onboard GPU.

When i startup my computer first time, it startups normal and works fine. When i restart my computer, on the BIOS logo screen it freezing. Then i shutdown it or unplug PSU cable from back side of computer. Then i connect it back and starting up computer. My computer starts normal. And then when again i do restart, the same problem.

I want to know my friends, what is the problem with my computer.

Thanks for help.