How to restore my boot up speed

[MichaelZ]

Windows Vista Home Premium 64-bit. SP2. Intel Pentium Dual CPU [email protected], 4.0GB RAM
For the last 5 or 6 days my computer has been very slow to boot up, taking anything up to 4 minutes from switching on to being usable. Previously I have been up and running in around 90 seconds. I have run CCleaner and also done a full scan with MS Security Essentials - to no avail.
According to msconfig my Start Up items are only Windows Defender, Microsoft Security Essentials and Registry Booster.
The only software that I have installed recently (Adobe Photoshop Elements 9 and Picasa) I have also uninstalled and neither of these items are showing in my Programs and Features so I am happy that the Uninstalls have been effective. I have also recently copied a CD of photographs (350MB) to my hard drive and subsequently erased it.
I have been advised by the so-called technical experts that the only solution is a complete reinstall of Windows but I am reluctant to do this for fear of losing valuable data.
Can anyone please suggest anything that I can do to restore my previous boot up speed?
Thanks in advance

[AlBags]

Check all the result entries carefully when you run it.
Look for 'file missing' among other processes.

[MichaelZZ]

Thanks for all your comments, Albags

I've just run a HijackThis scan and now have a screen and a half of results. There are prefixes R0, R1, R3, F2, 01, 02, 03, 04, 08, 09, 015 and 023. Many of the entries have (File Missing) at the side of them.
What exactly am I looking for?
Thanks and regards

[MichaelZZ]

Hello again Albags,
To answer your earlier points;
I have looked under regedit and can confirm that the line "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
S

ervices\Eventlog\Parameters" is not present.
Also when I go to "windows\system32\winevt" I find a logs folder with 49 items in it. Clicking on any of these gives the error message "Event log service is unavailable. Verify that the service is running"