Can a power supply cause shuttering in games?

OK i asked this before(i must be getting very annoying     ) but i was not so accurate of what i was trying to say. games like sims 2 and fear 2 and gta 4 shutters
but games like COD5 and crysis plays perfect close to max out!!!
every time my game shutters im still getting lots of fps like 35-70 in gta 4 but believe me you can still tell the shutter and its the same in sims 2 (real bad in sims 2).............it seems like a texture loading slow down

i do not feel like this is a cpu/gpu problem (hello sims2 this works fine on a intel graphics chipset)

it seems like a hard drive issue because when it does it my hard drive light going off like crazy.......

i defrag all the time and run disc cleanup
i have all patches and the most up to date drivers as always

heres the rest of my system
amd athlon 620 x4 OC to 3.25ghz
ati 4770
3GB going to upgrade to 6GB of ram soon
320GB hard drive 8mb of cache..70MB max read speed..60MB write speed max
asus m4a785-m
antec 380watt power supply
windows 7 32bit upgradeing to 64bit when i get 6GB of ram


i would really like any suggestion



someone said
Well it maybe because of your PSU,because AMD recommend a 450W or greater PSU for a HD 4770


i said
can a power supply cause this to happen i know i need to upgrade buti be happy if this was the issue because im getting A new antec earth watts 650watt soon

LOL even resident evil 4 shutters lame!!!!! i want to know the issue

people told me this
not the cpu
not the ram 3gb is enough....even though im still upgradeing
cant be my GFX card because my nvidia 9500gt work perfect on resident evil 4
my board is ok asus m4a785-m one of the TOP sellers on newegg


so this is what i have left
power supply
hard drive

im upgrading both but can anyone else add more!!