I can not get my laptop to turn on.

Files missing or corrupt.
I would re load windows.

You can either try to spam the F12 button upon start-up to directly select which device to boot from, or either F4 or Delete are the typical keys used to get into the BIOS and you can change the boot order from there to automatically select a CD drive device if it ever detects one.

This sounds like a hardware problem. The most common is a hard drive issue. On startup in the right hand corner you will see two options, choose press F12. this will bring you to a menu. search for run diagnostics test. select that option and it should tell you what the problem is. Then go from there and research the problem further. There is many different thing that could be wrong. but this is the first step in the right direction. Hope this helps.

If you have enough room on your drives, copy the Windows disc complete to the hard drive and run setup from the hard drive.

Try letting it boot, and look for restore from your start menu. Some makers put it there, others, when you try to access the D:\ drive, it invokes program to ask the user questions on restore....

Do be aware that you need Windows and all other programs' access codes, after a reload. Another option is to create a new user, give that user admininstrator rights, and delete any unneeded users. Also on the boot up, watch the screen carefully, each system tells you how to access the bios, did you try delete? All of the keys you mentioned, try without alt, not sure that works at that boot stage.

boot files are corrupt or missing....
try re-installing OS

You probably have a problem with your operating system and will need to install windows again. You need to find the Windows XP installing CD that came with your laptop and also the drivers CD.
If you have found it, put the XP CD in and restart the computer and when the message says "Press any key to boot from CD" appears, press a key.
Then follow instructions to install Operating system.
If you format your Hard drive, all your data will be deleted so it might be good to backup your data by removing the Hard drive and buy a 2.5" HDD reader and get all the data off before you format or reinstall windows

Usually a bad screen or video inverter.Sometimes the video card is bad even with a white screen instead of a black one.

If you go into the BIOS, is the hard drive detected?

Did you just install this drive from another laptop?

It doesn't make sense that it would try to boot to win98, since the original OS was XP Media Center to begin with.

Let me know, and I can help you further.

Sony eSupport - VGN-UX280P - Manuals / Specs / Warranty
http://esupport.sony.com/US/perl/model-documents.pl?mdl=VGNUX280P