Erreur de chargement du système d'exploitation

Hello everyone,

the title of my message has a déjà vu feel, I think. I have been searching the forum for a solution for a long time and I hope the answer hasn't been too well hidden.
If that’s the case, I apologize in advance.

Here is the problem

I am using a FUDJITSU Siemens 15-inch laptop
Pentium 4 (I believe) processor speed 1600MHz
512MB RAM
80GB non-partitioned hard drive
with Windows XP SP2

since today I keep getting this error message: "error loading operating system" every time I turn on my computer.

From there I, of course, tried to reinstall and format everything, but I can't manage to do it. Inserting a CD-ROM changes absolutely nothing.
Starting from that, I go into the BIOS, set it to boot from CD/DVD first (which was already the case) but nothing works, I still get the error message. A menu also offers me to choose the boot option, (I think this is exactly the same but I still tested it) I tried all the options:
CD/DVD: same message
hard drive: same message
removable devices: same message
Realtek boot agent: (I assume this concerns the network, since the laptop is networked) there the computer gives me a series of numbers, then it seems to scan something (or look for something) and the result is as follows:
PXE-E53: No boot filename received.
while searching online I found the meaning:
(on this site http://www.emboot.com/faq-pxe.shtml )

# Close list PXE-E53: No boot filename received.

The client received at least one valid DHCP/BOOTP offer, but does not have a boot filename to download.

But with all this I still do not know what to do
do you have any idea?

help

Thank you in advance