User32 Error

My server running Windows NT4 with service pack4 has been given some error messages for 2 days stating that the initialization of the dll library (C:\WINNT\Systems32\User32.dll) has failed and on the 3rd day my clients could not receive nor send e-mails on our intranet based on MSExchange 5.5.
I had to delete the IMS and add it again from the Exchange Administrator twice before the Internet Mail service could start again. This morning on booting Dr Wartson gives a Fatal error message -could not attache to the application Error Code=87. Though we could still send and recevive e-mails on our intranet. Pls can somebody help before the system crashes totally.

Jide