Good Morning,
It is never a good sign when your computer wont boot properly, first off is this a desktop or laptop
There are more reasons why your machine wont boot that we could go over here in a forum, from a cable being lose to the hard drive has gone bad. and or everything inbetween.
When you say you try to boot in safe mode, are you able to catch the screen flash at startup in order to get to the safemode option? and do you know what F key to hit. usually F8 is to get to the same mode option, if you can get there make sure you load it with networking so you can use the internet to help you diagnose the issue, incase it is software.
other F keys are F2 and or F12 for the startup bios menu and you can look there to see if your Hard Drive is being seen by the Bois at start up. it shoudl be listed as the Master drive or CS for cable select and it should have valid characters behind it and not things like #%$^, Garbage like this means usually the hard drive was not read properly and is probably bad.
Work arounds for not losing your data is to buy or borrow an hard drive, internal or external, if it is internal you can make it the master hard drive install your OS and after a reboot you should be able to explore your old drive and save your data, Most local computer stores will do this for you for around 25-50 dollars depending on your area.
if it is external you will need to had an OS already on it so you can boot from it. and again this will allow you to get to your data in most cases from the new drive.
If it is your machine and you are comfortable opening it up make sure you dust it out, check your cables for any lose connections and check the CMOS battery usually a CR2032 3.3v circular battery, my understanding is if the battery is dead the computer wont boot. at least this is some of what i have read.
Don
Good Luck getting it fixed.