XP Startup Problem

I apologise if this has been covered in other threads but I cannot find anything similar after a search.

I have a fairly new PC on which I installed XP home, everything was fine initially but then I started to have problems starting the PC.
Most days it would start normally but on other days the PC would hang just before it got to the XP splash (loading) screen. All I would have would be a black screen and the HDD light would go out. After resetting the PC I would get a message asking how I would like to start the PC, after choosing "start windows normally", the PC would start OK.
Between the PC working fine, and the problem starting, the hardware in the PC had not changed.
I then added a sound card to the system and at first the problem did not get any better or worse.
For the last week however, the PC hangs every time I go to start it and it can take 5-6 resets before the PC boots normally.
I've tried putting the PC into hibernation when shutting down but on re-start I get an error message about being unable to recover from hibernation and I have to re-start as normal. Then I get the same problem.
I've tried system restore and SFC but find no corrupt files.
I can boot from floppies and CD's first time every time and navigate the HDD so I cannot understand why I have this problem when booting into XP from the HDD.
Thinking it might be a power supply issue I've moved the PC to another socket - that didn't work.

I'm at a loss and would appreciate any ideas or suggestions.
Thanks.

 

This sounds like a boot sector problem . I would update the bios .boot the machine , go into bios select quick boot and if that didnt work I would run fdisk delete dos partitions . create new dos partitions format the hard drive and clean install os. This should narrow it down to software or hardware issues. This should only be done if you know how to do it properly. I am a tech so I look for the fastest ways to resolve problems. You may want to wait for other replys for a better way as you will lose all data on your hard drive.