No Power

I just put 512 RAM into a Quantex Desktop with P2. Also added burner. Wouldnot power on. Checked power supply. Fuse blown. Replaced power supply. Tried 300w ATX no power. Tried 145w AT power supply.no power. original p/s was 235w, seems to be AT no extra plugs. Cover is on connections checked. Got to be something simple??? PC has experienced surge(ligtning) but has been working. Thank you, Mark