Why does the bios automatically prioritize the network card on boot?

Question

Iron

Installed a second hard drive (SSD), instead of a DVD drive on a laptop.
When the system boots, sis191 pxe bootRom appears. Climbed into the BIOS, changed the boot order, it still starts loading from it. And with a new entry into the BIOS, the boot order changes and the network card is closer than the hard one, and therefore it is loaded from it.
What could be the reason and how to fix it?
UPD2 The problem is not the batteries, the date and time do not fall. Changed an unimportant parameter and boot order. It loaded, the boot order was reset again, but the parameter was not.
UPD1: Reset bios to default settings, didn't help. But now the flash drives are slow. You need to turn on USB 2.0 in the BIOS, but there is no such option. Flashing the BIOS, according to the manufacturer's website only with a paid utility (BiosAgentPlus).
Information on the board and bios:

Свойства системной платы:  
   ID системной платы   <DMI>  
   Системная плата   Clevo W760SUB  
   
  Свойства шины FSB:  
   Тип шины   Intel AGTL+  
   Ширина шины   64 бит  
   Реальная частота   200 МГц (QDR)  
   Эффективная частота   800 МГц  
   Пропускная способность   6400 Мб/с  
   
  Свойства шины памяти:  
   Тип шины   DDR2 SDRAM  
   Ширина шины   64 бит  
   Соотношение DRAM:FSB   10:6  
   Реальная частота   333 МГц (DDR)  
   Эффективная частота   667 МГц  
   Пропускная способность   5333 Мб/с  
   
  Свойства шины чипсета:  
   Тип шины   SiS MuTIOL  
   Ширина шины   16 бит  
   
  Производитель системной платы:  
   Фирма   CLEVO CO.  
   Информация о продукте   http://www.clevo.com.tw/en/products/index.asp  
   Загрузка обновлений BIOS   http://www.clevo.com.tw/en/e-services/Download.asp  
   Обновление драйверов   http://driveragent.com?ref=59  
   Обновления BIOS   http://www.esupport.com/biosagent/index.cfm?refererid=40

Answer 1

Make sure you change the boot order permanently, not one-time.
Generally disable PXE booting.

Answer 2

Maybe everything is much simpler, save on exit, or replace the battery.