Hi all I'm new to the forum and will post an intro as I intend on sticking around, but first I'm going to jump straight in with this post as I need to fix my PC as soon as possible and at the moment it's completely unusable. My problems started when I tried to upgrade from Windows 2000 to XP. Part-way through it rebooted as it should do, but then kept flashing a blue screen error briefly before restarting itself (the blue-screen error was something like "PAGE_FAULT_IN_UNPAGED_AREA"). Rather than mess around trying to resolve that problem, I opted for a clean install. This went without a hitch, and after a few hours I'd got all my stuff back on there (copied from a removable USB hard disk). I thought "I'll just run the disk tidy utility, then defrag and then I'm good to go". Big mistake! Disk tidy said there was about 30MB of temporary files that it was safe to delete, so I let it do its thing. Part-way through I got an error message saying that some of the system files had been replaced with "unregistered alternatives" (or words to that effect). It then asked me to insert the XP CD so that it could replace the files. I did so but it just kept saying that it couldn't find the files on the CD. I hit cancel and was returned to the desktop, only to see all of my shortcuts vanish, leaving only some folders that I'd created and some other stuff like the "My Computer" and "Recycle Bin" icons. I tried to open the start menu but it was all screwed up, and almost all of the usual stuff in there was missing (including the majority of icons on the control panel). I tried a reboot but now before Windows initialises it goes to a black screen with an error that says Windows root\system32\hal.dll is missing or corrupt, asking me to re-install it. I then tried booting from the XP CD again to run a repair installation but as soon as I entered XP setup it said "An internal setup error has occurred. No space for swap file". My understanding is that the swap file is no more than 1 Gb and I know for a fact that there's at least 20 Gb free on my C drive so I have no idea what's going on. I know that the last time it happened, I deleted my partition and reformatted C to solve it but I can't do that this time. I'm now completely stuck. I can't do another clean install because a lot of the stuff on C hasn't been saved onto my external HD (I only usually back it up when I intend on making changes) and I can't afford to lose it all. Can anybody help me find a way to get my PC up and running again?