Computer Start Up Problems?

I have bought a NEC L1040 mini tower with Vista Home Basic installed. Got it home started it went through the vista set up eg P'words it done a scan saying it would reboot once finished, finally shut off but no reboot. Switched on manually cooling fan just kicked off really fast & nothing else. Tried again got the error screen Start in Safe Mode or Normal went for Safe nothing happened. Started again same screen didn't recognise K'board or mouse this time. Once again fan just started nothing else, tried again got error screen went for normal, worked but had to set up vista again finally was on and all worked fine that day. Came back the next day and couldn't get it to boot up only the cooling fan would start really fast continually and nothing else happens. Rough Specs Intel Celeron D 1.6Ghz/800Mhz FSB 512MB DDR2, 80gb Sata HDD, Norton 07, Mcafee, Acrobat, Media players, so nothing flash just basic computer. Please help!!?