Hello! I really need help with this particular program

Yesterday, It
was working just fine. Last night, I just added a user in the accounts
then updated the mac os update. everything after that went haywire

Everytime i try to run the VPC, it would give me errors like "OS not
found...install an OS on this hard drive" and "Reboot and select proper
boot device or insert boot media in selected boot device"

I really dont understand whats going on since it was working perfectly
fine yesterday

Everytime i go to the PC settings to select from the
virtual PC list...all selections are gray

Btw, i have a G4 OS 10.4.5 now

I also did the disk repair utility thing...but still didnt work

i was able to run xp on VPC on another user's account but heres the thing... it gave me another error..Windows-delayed write failed-"windows was unable to save all the data for the file c:. The data has been lost. The errors may be caused by a failure of your computer hardware or network connection. Please try to save this file elsewhere."...meaning?

sorry...im really not a techy not to mention the fact that i am so used to PCs

Another error is this... Isass.exe-system error
an I/O operation initiatedby the registry failed unrecoverably. The registry could not read in, or write out, or flush one of the files that contain the system's image of the registry."
Also, I have 2 different files of WinXP pro.vpc7 that contains different sizes...1 is 2.34GB on disk and the other has the same file name but is only 3.3 MB in size...??
Another error just came out as well..."the primary disk image could not be written to. he image file may be locked. The disk has been mounted read-only. Most operating systems cannot boot with a read-only primary disk."
How can all this go wrong just by installing the update of VPC?

(
Please help!
hanks!