What am I do to Do?-Mac powerbook G4 Problem?

I have Tried everything but cannot solve this problem.

I know its an old mac and most call it absolute/vintage! but it worked fine, its just that it was real slow, so I sent it with someone to the US to get it serviced at an Apple shop-The guys there, told my friend that its a vintage and we can't do anythiing as we have no parts etc-Before I sent it , I had almost copied all my stuff on a thumb drive with 80GB capacity,, like bookmarks, the MS application, and as I was copying all the pics from Iphoto, it said 3058 items and after almost an hour it just froze, so I clicked on cancel-I checked the Thumb drive and noticed that almost a lot of pics were there-However Iried again but this time it came up saying ' this is being used by another application and I just could not copy them-Because I did have the pics in my email, I did not bother.

But then,suddenly I noticed that all the icons on my desk top, folders etc just vanished! I went in to the Zfinder and saw that they were there, so again I did not bother-

As said the guys at the apple shop told my friend that they have emptied the cache and it should be much faster, and to do this every 3 months press Ctrl or such ( I have not done it as it was done by them) On return, when I switched it on, I thought my folders and icons on the desk top would come up , but they did not-However in the Finder window I noticed that when I clicked on the Desk top there were just Jpg's and all say 0 kb.

I tried to delete them, move them to thrash but a message comes up , you cannot do this as its being used by another application, Stop or continue-despite clicking continue,nothing goes in to the recycle bin

I just cant seem to move them out!

What should I do? PLease help me someone-I am the only one who says the Mac is just so wonderful! the rest in the family are all Bill Gates friends!

I know its an old tiger10.4,

Please send me a step bystep guidance-THANKS A MILLION