strange behaviour after reset...

Hello,

I have some problems with my PC:

1. I Power-on the PC, Winodws XP is loading (fast loading process,
running fast after it was loaded)

2. Now I am reseting my PC (startshut downrestart)

3. From this point strange things happens:
Windows is loading very very slow (for about 7 min). After it was loaded
it is running extremely slow, harldy responses to the mouse click

4. I close Windows(startshut down) + I plug off my PC from the socket(this
is important to make the PC work well)

5. I connect PC to the socket, power on it. Now Windows is loading fast, and
running
very well after it was loaded...

Maby somebody has an idea of what is happening here??

Thank you in advance
Wojtek


PS.

PC configuration:

mainboard: ECS K7VZA rev 3.0
ram: 768MB
cpu: Duron 750 MHz
OS: Windows XP Prof