Well, "halt" is pretty commonly accepted now adays and from what I know it does flush the cache (a very old difference between a shutdown vs halt but I've never had any problems in the last 15 years or so doing a halt if it's supported).
Do you have a regular monitor you can connect to the system? A lot of operating systems will know that they weren't previously shut down properly and start a fsck (File System ChecK) which you might not see via terminal unless the OS is configured to redirect the console output to the serial port. Most likely your terminal is relying on the TAMS program running and listening on the serial port. If the computer has a video card (likely has a vga/svga card in it since we've established it's just a standard Intel based machine) you should be able to connect any 15-pin vga monitor to it and probably see the output while it boots.
Do you have a regular monitor you can connect to the system? A lot of operating systems will know that they weren't previously shut down properly and start a fsck (File System ChecK) which you might not see via terminal unless the OS is configured to redirect the console output to the serial port. Most likely your terminal is relying on the TAMS program running and listening on the serial port. If the computer has a video card (likely has a vga/svga card in it since we've established it's just a standard Intel based machine) you should be able to connect any 15-pin vga monitor to it and probably see the output while it boots.