The 115 means 115 volts. Check to make sure the 750W PSU is on the same setting and that EVERYTHING is plugged in properly. Remember the 4/8 pin Motherboard power connector, etc.

Different countries use different voltages. It's cheaper to make a switch & some circuits inside the PSU than make a whole new one.

I just bought an ultra lsp 750pro, 750watt atx power supply unit. I hooked it up started my computer and the fan turned on for about 5 seconds and my keyboard and mouse flashed, but after that the green light on my computer stayed on but the fan stopped running on my motherboard and nothing happens. Also on the psu that came with my computer it has a red switch with 2 settings "115" and "230." If I have it on 115 my computer runs normally, but if i swiitch the red switch to 230 on my computer's psu it does the same thing as my 750 watt power supply. So in conclusion I have 2 questions:

1. Will i be able to some way use my ultra lsp 750 watt atx power supply unit(It was a real good deal and had a lifetime warranty so i do wanna keep), and if i can't save it what psu can i get so i can run a radeon hd 4870(needs to be cheap as in below $70)?

2. Why does the switch only work on 115 and not 230?

Info:

This is my computer: http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=4555150&CatId=5140

Im pretty much stuck with that computer and i really want to use my radeon hd 4870 :)

Thanks in advance.