I've just been given a 'puter to fix. Won't run anything by the looks of it. I've just got the bare box so plugged in spare monitor k/b mouse and booted up. Windoze will not recognise the mouse, so I must use the k/b to browse the machine. Every time I try to open an app, e.g. MBAM (in this case from memory stick) all I get is a popup Internet Explorer Downloads window. I tried stopping all non essential services but still won't work. My next trick will be to boot from a live CD and, hopefully, see what caused the issue.
XP? I'd suggest the old non-destructive reinstall. But... No Windows update, now.
No..W7, I, at least, managed to get back into the machine enough to run some scans. MBAM has cleaned out some stuff, now running combofix.
There is a repair facility on the W 7 disc, have you tried safe mode I think it's just tapping F 5 while booting up, maybe with the the disc in worth a try