2 problems with my Latitude LS H400ST

I dont know if somebody can help me on those ones. I have 2 weird problems with my laptop Latitude LS H400ST which i cant fix. The first is after updating my bios with the latest version which is A09 it became a tiny bit corrupted but only in the boot section. I cannot chose to boot from network anymore (which i used to acces the laptop because it didnt had external drive). Now i have only 3 choice... First is the Hard Drive second is unreadable garbage and the third is removable disk.I`ve tried to downgrade my bios to the original version A05 but the problem remains and i dont know what to do anymore. Greatfully i had the idea of installing dos and windows which bring me to my second problem. At a certain point during windows 98 installation (which is the detection of material) windows become incredibly slow and it take alot of time to finish the setup. Afterward, i can boot windows up but at a certain point of the boot (After the destop has appeared) all become very very slow and it`s literally impossible to do anything. I`ve tried the Dell Diagnostic tool but it doesnt find any error from the hardware (I`ve done the extented test by the way) I hope someone can help me fix these problemes. I`m not a rookie at fixing pcs as i have a degree in it. I`ve tried many thing but i can figure the second probleme out. It seem that windows loads a drivers the does correspond to the hardware but isnt done for it, slowing everything down making it impossible to install anything or even open the Windows explorer.

CPU : 400MHz Pentium 3

RAM :128 MB