comp shuts down after selecting start comp normally or last known config selected , same as safe mod

Tshufeldt

well yesterday i was just watching some movies on my comp and right when i was about to shut my comp down selecting the start menu it just shut off i didnt think anything off it at the time i was tired . but this morning when i got up to turn my comp on i couldnt get passed the screen were it asks you to "select last known config " or "start windows normally" or safe mode ect , iv cleaned all the dust out my comp and wat not still didnt fix the problem the cooling gel on my cpu looks a little out dated but not that bad but still after selecting one of those options start normally or last known config it just shuts down and i have to click the power button again but still cant get past this screen , i was able to get to my desktop 1 time then all the sudden did the same shutdown and i was back to the drawing board i thought it fixed itself but no just got further than i ever had .. i cant even use my comp somone help before i take it into PC club ,
have 3 g of ram pc 6400 ddr2 2.4 x2 duel core athalon , gforce 7800 EVGA video card ANTEC power suply not shure wat the problem is somone help please