Corrupt HIMEM.SYS

I have P-III 750 MHZ with WIN’98 loaded on it. While starting up the system gets rebooted again and again. My investigation shows that while loading the HIMEM.SYS this rebooting is happening. I had tried replacing the existing himem.sys with a freshcopy but to no avail. If i boot the system thry step-by-step confirmation mode and bypass the device=himem.sys directive, it boots to command prompt without any problem but windows won’t load due to non availability of himem.sys file. Please help.