So my computer is not working - the disk is totally cleared, I've deleted GRUB and PLOP which I used to install new system, because CD-Rom is broken and BIOS is old (whole computer is old, it's Sony Vaio PCG-GR250) so it won't allow me to do it via USB and I got no floppy drive :) the only way is to PXE boot PLOP and install Linux from USB after PLOP has been opened. (I'm not a specialist but that's how I see it) I'm using Mac OS X 10.9 and I followed number of tutorials how to set up TFTP and DHCP server and I got PLOP here, but when I boot up with PXE it says that it found DHCP but TFTP timed out. Any help or alternative way of rescuing old laptop? Thanks in advance!
You can move its HDD to another machine, install full system or just grub, then move it back. Linux have all drivers, so in most cases it will boot without any problem.
Another way, by using USB/IDE adapter, if you can't mount in the other machine or not allowed.
With Grub2 and enough RAM, you can setup Grub ISO Boot. So you can install new system without need of any external device. See Grub2/ISOBoot/Examples
Advice, better to make a separate /boot partition. If new system installation failed, you have a grub boot at least.