Reboot immediatly after I enter any command in grub shell.

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Hi,all
                I meet a very strange problem.
                Yesterday I bought such a PC:

        cpu:    PIII 866EB * 2
        mainboard: SuperMicro SUPER 370DLE
        memory: 256M * 4 ECC
        harddisk:       Maxtor 92049U4, 19541MB w/2048kB Cache, 
CHS=2491/255/63, UDMA 

I installed redhat 6.2 on it. Then I installed grub 0.5.96.1.
I typed the following command to install grub on my disk

#/usr/local/sbin/grub-install /dev/hda

After I rebooted my pc,I got the grub shell.The problem is:
1.If I input any correct command such as "help kernel root...",after I press 
the "enter" key,
system will print the correct respond and reboot immediatly.
2.If I input some error command.system will print "Error 27: Unrecognized 
command".It will
not reboot.
3.If I press tab key,it will display the command list and will not reboot.

Because of the problem,I can't boot to linux.

Then I boot from a rescue disk,and edited a menu.lst in /boot/grub. This time 
grub will not
fall in the shell prompt,it will directly boot my pc to linux.



some more systeminfo:

#lspci
00:00.0 Host bridge: Relience Computer CNB20HE (rev 06)
00:00.1 Host bridge: Relience Computer CNB20HE (rev 06)
00:02.0 VGA compatible controller: Cirrus Logic GD 5446
00:06.0 Ethernet controller: Intel Corporation 82557 [Ethernet Pro 100] (rev 08)
00:0f.0 ISA bridge: Relience Computer: Unknown device 0200 (rev 51)
00:0f.1 IDE interface: Relience Computer: Unknown device 0211
00:0f.2 USB Controller: Relience Computer: Unknown device 0220 (rev 04)
01:02.0 SCSI storage controller: Adaptec 7892A (rev 02)

#fdisk /dev/hda
Disk /dev/hda: 255 heads, 63 sectors, 2491 cylinders
Units = cylinders of 16065 * 512 bytes

   Device Boot    Start       End    Blocks   Id  System
/dev/hda1             1        66    530113+  82  Linux swap
/dev/hda2            67       192   1012095   83  Linux
/dev/hda3           193      2491  18466717+  83  Linux