Help!!!! My computer is acting weird!!!

[jinkds]

My friend just built a new system for me.
here is the system:

AMD Athlon 64 3500+
MSI K8N Neo2 Platinum Socket 939
eVGA GEFORCE 6800 GT
CORSAIR 1GB (2x512) TWINX1024-3200XLPT 1024MB XMS3200
Seagate ST3200822AS Barracuda 7200.7 200GB Hard Drive X2

here are the problems... When I first turn on the computer the mouse doesn't work
but after I restart it by pressing the restart button, the mouse starts working.
Also when I play HL2, it keeps stalling for about 3 seconds very often.
does anyone know what could be causing these kinds of problems?
help....

 

[amol]

about the first thing . . . is the mouse connected into the USB port or into the special mouse PS/2 port?

 

[jinkds]

PS/2... but the keyboard is USB. My friend suggested me to try both with USB...