Hi @tarikutenaye
It's trying to boot from an external server connection (PXE) which obviously is not there that is why it takes so long.
Check that the coin cell battery on the motherboard is OK. This battery maintains the BIOS settings when the PC is turned off and when it gets too low the BIOS can become corrupted which can cause problems. These batteries are a non rechargeable Lithium battery and usually last from 4-6 years
Turn off the PC and disconnect the power from the PSU. Open the PC and then remove the coin cell RTC battery from the motherboard and measure its voltage. If it is <2.5V DC replace it. The battery type number should be printed on the battery. Usually it is a CR2032, available most everywhere. Here's the [https://dl.dell.com/manuals/all-products/esuprt_desktop/esuprt_optiplex_desktop/optiplex-7010_owner's%20manual4_en-us.pdf|owner manual] for one variant of your model that may help. Go to p.15 to view the procedure
Reinsert the coin cell battery (usually +ve on top as marked on the battery) reconnect the power to the PSU and turn on.
There may be a message that the date and time is wrong. This is normal as the BIOS has been reset when the battery is removed for long enough i.e. >5 minutes. The message won't appear the next time that the PC is started.
When you first start the PC, get into the BIOS boot menu on startup by pressing the F12 key a few times when the PC starts.
Make sure that the HDD (or SSD whatever you have installed) is the ''1st boot option.''