Try this: Hold down the ctrl key before it starts to boot. When you get the boot menu, choose command prompt only. Then edit your config.sys file.
Add these 3 lines.
DEVICE=C:\WINDOWS\HIMEM.SYS
DEVICE=C:\WINDOWS\EMM386.EXE NOEMS
DOS=HIGH,UMB
These must be the first three lines in c:\config.sys...