BLUE SCREEN ERROR missing usp10.dll

Clarifications

Well since you can't even get into safe mode you only have 2 choices.

1) Attempt a repair installation of the OS. This would save the program file and data from being lost.

2) If that fails your only other choice is to format and start over.

Now if it comes to that you should be able to set the OS up in a dual boot so that the data is still there. The programs would need to be reinstalled but the files will be safe.

Best of luck

to get there you need the XP installation CD in order to get to recovery console in order to be able to copy files to the PC

On one particular SP2 system in the c:\windows\system32 folder that file has
the following attributes.
USP10.dll
version: 1.420.2600.2180
Size: 397 KB
Date Modified 8/4/2004

You could try copying that file from a working system that that has the same
version of XP with same service pack level to a CD, then with the XP
installation CD, and booting from that enter the recovery console. Once
there copy the file from CD to the C:\windows\system32 folder.

How to install and use the Recovery Console in Windows XP
http://support.microsoft.com/kb/307654/en-us

If that doesn't work then you're next option is to restore XP using the recovery method that came with your system. Normally this is a destructive recovery (All data and settings will be lost.

If you don't have a backup, then you would need to mount your drive as a secondary drive on a working system to access the data.