About all I can recommend is to remove all partitions and start over with an OS meant for that system. If it has a product ID sticker and you have the Vista recovery software, that would be easiest. If you don't have the disks, you could contact the manufacturer to see if they are available for purchase.
Given Presario C500 without hard drive,had Vista originally. Installed Samsung drive HM160HI. Friend?, installed xp pro OS. Later while installing programs, I would get " cannot complete installation because invalid windows system". For a short while could go on-line but performance declined, then couldn't connect with usb modem, dial-up or cable modem. Looked at system properties and saw "error" for Sierra wireless adapter, Wan miniport, realtek ethernet NIC, cricket USB wireless adapter, AVG miniport driver and network controller. Also have numerous Status "Degraded" on drivers,netbios,proxies,protocols,translaters,classifiers and more.
Should I FDisk and try loading Vista???
Any comments or suggestions will be GREATLY appreciated!!!
Thanks from missed the computer by a generation.....