salam guys i have hp dc5100 pc

yar system mai yeh problem aa rahi hai system bar bar restrat ho raha hai

windows bhi install nahi kar paa raha or pehly jo windows install this us per bhi restart ho raha tha

mai ny ram bhi change kar k dekh li pc bhi clean kar lia liken system bar bar restart ho raha hai kabhi system on karo to 2 ya 3 bar bios per hi restart ho jata hai

to kabhi system 30min baad ya 15min baad restart ho ta hai
kisi ko pata hai yeh masla kia hia ?

spec...

2.8ghz p4
1gb ram
160gb hdd
cd rom