OMG, what a stressful night. Yesterday evening, I went to a teaching academy to install Linux (Ubuntu was the distribution of choice) on all their 12 boxes. I started by resizing the FAT32 partitions, continuing with the Linux installation. (Stupid me because I did no test in the middle.) After two hours and a half, I had all the machines up and running, and I was surprised to not have had any problem.
But I was completely wrong. I rebooted one of the machines to check the network setup in Windows... and it couldn't boot! No error messages, no disk activity... nothing. Ugggh... I started trying everything I could imagine: fixmbr and fixboot from the recovery console, chkdsk /p, restoring ntldr and ntdetect.com from the installation CD... without no improvements at all.
After an hour and a half of tests, the academy had to close, so I had to go home... extremely worried because they had class this morning and needed the computers. At home I started doing tests on my own box: resizing the partition (which didn't break the system), using a boot disk, installing Windows in "recovery mode" to see if it could be useful to solve the problem...
I had some hope in thinking that a boot disk could help, but this morning it has proved to be useless. But luckily, I found the solution after reading some pages in Internet that talked about similar problems. The BIOS was set up to automatically detect hard disks and, for some strange reason, they were detected as CHS. I manually switched them to LBA and... voila! The systems started working again without no problems.
Now I wonder why the hell they could boot before all the changes in CHS mode, but not after. Anyway, I'm now a bit more calm, but this has really been a very bad experience :-/