Computer. My computer says that NTLDR is missing. I was told to use the reboot cd but i wasn't

Question

My computer says that NTLDR is missing. I was told to use the reboot cd but i wasn't given one because best buy told me i didn't need one. I am not about to buy something to fix this problem since i already spent so much money at your store because nothing seems to ever work right. I am getting very tired of my computers crashing and I buy them through you so i hope you can help me. I also have a dell computer that i bought through dell and have yet to have a problem with it.