On starting up screen says ntldr is missing press

i need to os platform..however assuming that u r using win xp pro sp2 or higher..n hope u r a professional..

this is a case of os corruption or the file which is hidden under <root system directory, usually c:>..is deleted somehow..!!..may b a virus/trojan or hardware or software is responsible..

probably now u got two way out:
1) copy the file in windows repair mode or from any identical os n put it in place as stated above..
OR 2) reinstall os.. (to take data backups u gotta connect the hdd to another pc/laptop, for such cases a hdd-case is available in the local spare market, it'll make behave ur hdd to act as an external removable drive)..

this can also b a symptom of faulty/defective of RAM..pen clean/remove carbon & or oxide formed on the teeth with an eraser n resit it..[it'll b more prominent, that if itz cause by ram or not,..if during normal operation, a Blue Screen appears/Memory Dump]
though, sometimes itz also caused by the m/b..

always better to seek professional advice of ur system admin/vendor....

This may indicate that a file is corrupt. First, make sure there isn't a disk in the DVD drive (trying to boot from it) or any USB hdd or flash cards plugged in.
If everything is clear you will have to do a repair on your system. Insert your operating system cd and follow the prompts to do a repair. If your running Windows, during the start up it will ask if you want to do a repair using Recovery console (say no at this point - unless you feel comfortable copying the ntldr files from the cd to your hard disk) the one you want is in the next section after pressing enter. Do

Hope this helps.